|“||Now cry, scream and beg for your life! Show me the despair on your face!||”|
—Zack to Rachel in Episode One
|Also known as||
Isaac Foster (Real Name)
186 cm (6'1")
Rachel Gardner (Ally)
Nobuhiko Okamoto (Adult)
Zack 「アイザック・フォスター」 is the deuteragonist of the game, manga, and anime, Satsuriku no Tenshi. He first appears as an enemy of the B6 floor when meeting Rachel Gardner, and then an ally throughout the course of the game.
He is a serial killer who is currently on the run due to his connections with recent murder cases. At the end of Episode 4, Zack was originally set to be executed, but he later escapes.
Zack is a tall man who is estimated to be in his 20s according to his records found by Rachel in a secret backroom on the B4 floor. He wears a brown hoodie with a zipper that's stained in blood, red pants, and black shoes. His whole body is covered in bandages which are used to hide his burned skin. His weapon of choice is a large scythe which he uses to cut down things that are in his way, whether if it is for killing, destroying objects such as breakable rocks & tombstones, or walls. He is also shown to have wielded a knife, which he previously used before coming across his scythe.
As a child, Zack's hair was much messier and had a tacky short-sleeved shirt and short pants.
Zack has anisocoria, a condition in which the eyes are unequally dilated. It is widely speculated that the abuse he received at the illicit orphanage is the main cause of this condition.
Zack often speaks in foul language. He will occasionally swear in the situations he's in, and will not hesitate even if it is towards Rachel, despite her young age. It is also revealed that Zack never had any education of the sort, as hinted in his inability to read, and when characters in the story explain things to him in long terms that makes Zack frustrated and unable to understand unless if it was explained to him in simplest terms. Because of his lack of knowledge and education, when he is put into a situation which requires using the brain to figure something out, he often forces upon Rachel to do the problem-solving.
Zack has a mental disability, whether it was something he had since he was born or he developed at some point in life is uncertain. This disability consists of him having a lust for destroying things, even to the means of killing. His blood rushes to a certain point and causes him to lose control of his urges. He will go into a short phase of destroying anything in his way until he's satisfied or until he rehabilitates.
However, it can be regarded that while Zack is not academically intelligent, he is high in instinctive/survival intelligence, where he relies on his instincts to get him through situations and can be seen as clever. Which could be how he was able to survive as a child, and up until now. And perhaps can even be described as an animal in a way. Zack is also extremely strong and rather fast, being able to run at rather incredible speed rates, and overall is actually a rather powerful character, which balances out the fact he isn't that smart. Zack is also very brutally honest, as he hates people who lie with a burning passion and never ever sugarcoats anything he says. He also hates being ordered around and told what to do because it makes him remember his past where he was seen as nothing more than a tool by his caretakers.
Zack has come into terms with being viewed as a monster due to his bloodthirsty and strength, and by accepting it he is able to see himself as 'normal'. Despite this, however, there was a time he wonder what it means to be a "human" if he is not one.
As a child, Zack was much quieter and reserved due to the abuse he suffered and obediently follow whatever his caretakers told him. After he couldn't take the abuse any longer and killed them after being inspired by a horror slasher movie he watched, Zack developed an impulse to kill, particularly people who are happy as he believes that they are the ones responsible for making him the way he is. Because most people in the he knew in his life treated him horribly, experiencing kindness feels alien to him, resulting Zack became confused and irritated when someone being nice to him.
HistoryZack's real name is Isaac Foster. When he was still a child, his mother's lover tried to burn him and his mother alive for unknown reason, but he was resilient at that moment, and thus survived the burn. However, Zack remembered that not long afterwards, his mother wrapped him with clothes and then left him behind in care of a pair of orphanage caretakers for money.
Since then, he stayed in the run-down orphanage where children were likely to die, and the trafficking was illegal. His caretakers were rather abusive, even "forgetting" to give food to the children for multiple days, forcing Zack to dig through trash in search for food to survive. They would always refer to him as a monster because of his burns, even forcing him to bury the corpse of a dead child (was implied that he had buried others before as well) simply because they didn't want to deal with the smell. Zack himself, despite not wanting to, do what he was told without question.
That was until one day, when one of the caretakers left the TV on showing a horror film that included a serial killer, a film that the said caretaker liked. Zack just-so-happened to stumble upon it while it was on, becoming fascinated with the murderer specifically in the film. He took inspiration from it and he murdered his caretakers by repeatedly stabbing them before mutilating their bodies, later burying them in the back of the orphanage. This was most likely because if that happened in the film then he could do it as well, making Zack think that if he killed them, he wouldn't have to live the way he did anymore and that would be an easy way out for him to finally be free from his miserable everyday life.
After disappearing from the orphanage, Zack wandered on street and made his third kill by killing a woman who accidentally got him soaked with her car. Zack took a night rest inside her car and then was found by a blind old man the next morning. Passed out from exhaustion, Zack woke up in the old man's house who took him out of whim and then offered him a bread. While Zack was suspicious of the old man's hospitality, he still ate the bread as he hasn't eaten for days.
Since he didn't have any place to stay, Zack stayed at the old man's house, everyday spending his times sleeping or spacing out. Despite living together, Zack hardly talk with the old man. Zack found his new days freely without any need to think and ate the bread given by the old man who picked it specifically for him. Over the time, however, Zack became confused by the old man's kindness who unlike the adults he knew only viewed him as a tool. This gave him a shivering feeling that disturbed him and Zack believed the only way to repress it is by continuing his killing spree. He contemplated on killing the old man, but thinking it would be meaningless if the old man remains expressionless, so he instead went outside and killed a drunkard. When he came back, Zack admitted of the killings he had done, thinking it would make the old man afraid of him. To his surprise and confusion, the old man simply asked him what he wants to do from now on and told him to sleep.
The next day, the old man used the money he had saved to buy a better bread for Zack while determined to take care of Zack from now on, thinking his life finally has a meaning by caring for the boy. Unfortunately, on his way back, he was confronted by a pair of thugs who killed him for his wallet. With the old man unusually late coming back, Zack grew frustrated and started breaking the furnitures in the house, thinking the old man had abandoned him. By a chance, he found a knife and unable to hold his urge to kill any longer, Zack went out to kill. As he run to start his kill, he passed by the same pair of thugs who claimed to have killed the old man, breaking the crane that the old man usually carried. Seeing their happy faces that reminded him of the movie, Zack killed them with his new knife. As he was repeatedly stabbing them, Zack came into the realization that he only gets satisfied when he kills people who are laughing happily and fills them with despair, deeming those people are what create monsters. Accepting that he has become a monster himself, Zack decides to continue his killing spree.
Years later, his recent killings became quite famous, making him a currently wanted serial killer and criminal. He was eventually found by the reverend, Abraham Gray, who offered Zack the chance to stay in the abandoned building prepared by him as the master of the floor B6. Since Gray said that he was allowed to kill anyone who would enter his floor without having to deal with the police, Zack accepted the offer.
Zack first appeared as an enemy trying to hunt down Rachel on the B6 floor, his own floor. He killed a little bird that Rachel tried to tend and take back with her before giving Rachel 3 seconds to run away from him. Rachel hid inside a box in a room. Zack entered the same room and guessed she was hiding inside the box, but when he strike it and got no respond, Zack thought Rachel was not in there and left. However, Zack decided to return to the room and opened the box, finding Rachel's strands of hair inside, prompting him to continue his pursuit. He later found her near the elevator and locked the door so she couldn't escape, but Rachel turned off the light, blinding Zack's vision and managed to escape to the elevator.
- B5 - Hospital
After finding the bird he killed stitched and buried by Rachel, Zack decided to break the rule and chase after her to B5 floor, which belonged to Dr. Danny. He saved Rachel, who is trapped by Danny, by killing the latter. He was about to kill Rachel again, but finding Rachel has lost her will to live, Zack against killing her as it wasn't fun and it was against his ethic as 'grown-up man'. Then because of his violation of the rule, he became a "sacrifice" along with Rachel, giving the other floor masters to permission to kill him. This prompted Zack to try to escape B5, but he was stuck because the elevator did not work. Soon, Rachel showed up, asking him to kill her. Zack at first was disgusted, but after Rachel helped him get the elevator to B4 working, Zack offered that he will fulfill her wish if she helped him escaped the building since he is not smart enough, forming an alliance between them.
- B4 - Graveyard
In B4, the two entered rooms filled with graves. Zack, who is not good at solving puzzles, forced Rachel to do the brain work. Rachel then found a crack that led to another room. Because Zack can't fit into the crack, he let Rachel do the job again. During Rachel's exploration, she found a door that requires some sort of mechanism to open it, she tells this to Zack and went back to the room to solve the mechanisms. Meanwhile, out of annoyance seeing his own grave and boredom, he destroyed all the graves in the floor with a pickaxe he found, but left Rachel's grave as it was because she asked him not to. Then, under one of the graves he destroyed, Zack found a switch and turn it, which is the mechanism that is needed to open the door Rachel is struggling with.
After a while, Rachel came back with some documents about Zack's history as serial killer. Zack confirmed what the document said was true and questioned whether Rachel is afraid of him or not. When she claimed that she is not afraid of him, Zack was skeptical as he once killed a victim who tried to get away from him by lying she was not afraid of him. However, Zack then immediately remembered that Rachel wishes to be killed by him, hence, explaining her lack of fear of him, which furthered shocked him when Rachel added that she is not afraid of him because they have just met despite having read his document. When Rachel revealed she heard a child's voice that said he knows what her wish is, Zack realized that the master of floor B4 intends to kill Rachel, so he finally destroyed Rachel's grave while telling her that she only get to die after they get out of the building.
Rachel led Zack into a pressure plate under the water and told him to step on it to activate some sort of mechanism. While stepping into it, Rachel once again asked if Zack is truly going to kill her as he promised. The subject prompted Zack to ask the girl why didn't she just commit suicide herself if she wants to die so badly. Hearing Rachel's answer, Zack tries to get Rachel to make a face that will make him want to kill her, telling her to get angry or sad. Unfortunately, Rachel's expression remained empty. Zack then told her to smile. Upon seeing Rachel's smile, Zack finds himself stunned before snapping out and said her expression was no good because her eyes were still dead.
While Zack remained stepping on the pressure plate, Rachel returned to the room to find a way out. Later, when Zack hears an engine sound and unable to bear the cold water, he went back to the room where it has the cracks that Rachel went in. There, he encountered Eddie, the owner of the B4 floor. After hearing Eddie's wish of killing Rachel himself after falling for her at first sight, Zack tried to kill Eddie, but Eddie easily dodges Zack's attack and uses his control in the light source of the floor to turn off the lights, which let Eddie escape in darkness.
Knowing that Eddie is now trying to hunt Rachel down, Zack tried to call Rachel back but failed because Rachel can't hear him since she is in on the inner room inside the crack. Zack then arrives at another room with a small crack, which just so happens to be connected to the room where Rachel is in. Rachel, on the other hand, is with Eddie, who is trying to convince her to let him kill her. Just as Rachel contemplating to be killed by Eddie instead, Zack convinced her not to let anyone kill her but him by swearing to God that he will kill her. With their oath formed, Rachel told Zack to break the wall between him and the room behind it, reuniting him with Rachel. At this moment, Eddie immediately escaped.
- B4 - Power Room
Zack and Rachel continue their pursuit for Eddie and arrives at a power room and the elevator to the next floor, before it is a maze. Eddie shows up and turns off the power completely, which puts the room in darkness. Zack sends Rachel across the maze to find the power switch while he slows Eddie down using only his instinct, and if possible, kill him. Rachel successfully finds the power switch before Eddie can catch up to her and turns the light on. Eddie, now without the darkness to help him escape, is powerless against Zack, resulting with Zack killing the boy. Zack then throws his body down the hole of a big grave that was meant for Rachel, and blocks the hole with the gravestone. On the back of the gravestone, there's a switch for powering the elevator. Rachel pushes the switch and activates the elevator. They then ride the elevator which leads them to the next B3. During the ride, Rachel asks Zack if she is being useful to him, and Zack replies that she's a little bit useful.
Upon entering the B3 floor, the duo is already facing a problem of a locked iron barred barrier. Zack asked if Rachel can open the lock using her needle, but to his disappointment, she can't. However, flying bullets immediately take Rachel and Zack by surprise. Fortunately, Zack is fast enough to pull Rachel out of the way of bullets before it could hit them. The floor master, Cathy, introduces herself from the communication room while observing them through cameras and takes instant fascination for Zack whom she views as an exemplary sinner, much to Zack's annoyance. Cathy reveals that they can only continue unless they can continue from one door to another by passing the punishments she has prepared for them, which consisted of electrocution, poison gas, syringe, and gatling guns.
At the electrocution punishment, Zack becomes impatient after Rachel couldn't find anything that could help them out of the room, leading him to accidentally sits on electric chair (the only chair without occupants in the room) that usually used as death penalty for prisoner through electrocution. Cathy electrocuted Zack until to the highest level continuously while Rachel tries to find a way to stop the electrocution. Fortunately, Rachel managed to stop the electrocution on time by cutting off the head of the dummies placed there, saving Zack.At the room filled with poisonous gas, Zack gives Rachel the mask as he thinks she needs it more than him, but Rachel refuses and both agrees to trade the mask when they need it. However, after seeing Rachel forces herself and is close to lose her consciousness, Zack breaks the mask and help Rachel to a hold of herself, allowing her to find the keycard that'll help them escape the room. As Rachel is already too weak to move, Zack enter the keycard himself, but he enter it the wrong way, causing the card to break. Without any choice left, Rachel forms a new way out, though she was unsure herself this would work. Since they were dying anyway, Zack urges Rachel to go through with her plan. By using batteries and wires available there, Rachel resorts to blow up the whole room by using the gas itself since it was flammable, something that Zack was not fond of. For that reason, Rachel and Zack took their chances by hiding inside a big safe until the whole room explode, opening the door out.
On their way to the next room, Rachel is still worn out due to the gas, slowing down their walk. Zack refuses to go ahead of her because he needs her, so they decides to take a rest at the corner where the camera won't see them. While waiting for Rachel who falls asleep, Zack is starting to get irked by Rachel's behaviour who despite being smart is acting like an emotionless doll. This in turn makes Zack wonders why he is so bothered by it. The aftereffect of the gas then got the better of him, causing Zack to lose his consciousness and falls asleep as well. While sleeping, he starts dreaming about his childhood when he was still treated as a tool at the orphanage, angering Zack when he wakes up.Reaching the next room, Cathy offers Zack and Rachel a chance to live eternal imprisonment, which Zack flat-out refuses. Zack's mood worsened when Cathy taunts them by pointing out the fact that both he and Rachel are using each other as tools, once again reminding Zack of his past at the orphanage. The reminder causes Zack to take offence at Rachel's suggestions to avoid traps that he takes as her ordering him. Zack is further frustrated when they are faced with a choice of injecting two syringes (one contains strong possibly lethal dose) at the same time to get to the next stage. Zack refuses to play into Cathy's hand, but also disagrees with Rachel suggestion that she'll inject them both to herself since she may die and he won't be able to get out. He then questions Rachel what will happen if either of them dies, but Rachel doesn't know herself of the answer.
Seeing Rachel seemingly willing to take a risk of dying despite having already promised to help him get out of the building and be killed by him, Zack distastefully admits that Cathy is right about them using each other as tools for their own goals regardless of how they view one another. At this time, he also realized that the reason Rachel's behaviour constantly annoys him is because she reminds him of his old self who always did exactly as the orphanage caretakers told him without question. Refusing to be used by both Cahty and Rachel and putting their escape from the building as the first priority, Zack decided to inject both syringes into himself while ignoring Rachel's objection.
After injecting the syringes, the strong dose triggered Zack's past memory when he first killed that consequently also strengthen his urge to kill. When he and Rachel were in the same room again, Zack exclaims how he wants to kill so badly that it's driving him insane, pointing his scythe at Rachel. For a moment, Zack almost momentarily lost to his urge to kill, but is able to barely hold himself back after Rachel's voice that questions his true wish reached him. Recalling his own vow that he would never lie ever since he first killed people, Zack pleads to Rachel not to be killed by him as he has promised that he will kill her only after they get out of the building, not wanting to become a liar that he hates.
Following Zack's plea, Rachel tries her best to escape from him while he is chasing after her until they end up in a huge room with a few gatling guns pointing at them. Before Zack could kill her, one of the gatling guns grazed his arm, stopping Zack. Cathy then finally reveals herself, giving Rachel a chance to fight against Zack by giving her a gun. Zack tells her to make a shot while he is still able to hold himself back from killing her, but Rachel refuses because she doesn't want to follow what Cathy wants them to do. Rachel firmly tells Zack that neither she nor him are tools like Cathy said they are, and whether kill or to be killed, they were the ones who decide it.
Hearing Rachel's answer allows Zack to momentarily regain himself, impressed by her words. Not wanting to kill Rachel while she still has a boring expression and then get killed by Cathy, Zack resorts to use the reflection of his smile on the blade of his scythe to make himself cut his own stomach, deeming it as the best option. Despite the bleeding, Zack is still alive. This causes Cathy's attention to focus on him and gives Rachel the opportunity to shoot Cathy with her own hidden gun. With her guard down, Zack stands up and cut off Cathy's right arm that is holding the gatling controller before she could shoot Rachel, allowing Zack to kill her for good.
With Cathy dead, Rachel finally could safely approach Zack and asks him if he cut his own stomach because he feels happy as he claimed to be. Zack replies that he thought it was the best option so that he didn't need to kill Racher nor being killed by Cathy before laughing in delight at how Cathy was taken by surprise by Rachel's shot that gave him the chance to kill her. Zack then readies to head to the next floor, causing Rachel to worry as he is still injured, but Zack tells her to worry about herself more. While at the elevator, Zack asks Rachel how she ends up at the building and how she got her gun. Finding about that she has the gun all along after she witnessed a murder, Zack asks why she didn't use it earlier, but Rachel simply repeated what she said before: she won't commit suicide and that Zack is the only one who can kill her. Not wanting to bother with too much thinking, Zack shut down the question at that and praised Rachel for her action, getting into a good mood, to which Rachel pointed out. When they finally reached B2, however, Zack lost his consciousness due to his worsening injury, forcing Rachel to have to pull him out from the elevator.
As Zack sleeps due to his injury, Rachel goes to the room of the floor by herself. When he awakes, Rachel is nowhere to be seen so Zack tries to look for her by dragging himself, which worsen his injury until Rachel returns after meeting Grey. Zack scolds her for going alone and she should have woke him up. Hearing that Rachel wants to go back to B5 to get medicine alone, Zack tries to force himself to stand up so he can go with her, but quickly stumbles again as he lost strength. Rachel insists that Zack rest while she goes alone so she can be useful for him. Zack is against this again, but after seeing Rachel pleading so much, he finally relents under condition that she must come back alive while admitting that he'll only be a burden if he goes anyway with his injury. Before Rachel goes, Zack ask her to go to B6 and bring something from the room where they first met.
While waiting for her, Zack falls asleep again to save his strength. Sensing Danny is nearby and intends to kill him, Zack instantly awakes and attack Danny before the doctor could. Shocked to see Danny still lives, Zack then learns that Danny has prepared a safety measure to block Zack's attack and hid fake bloods to fake his death after having anticipated Zack would chase after Rachel to B5. Danny then questions Zack where Rachel is, to which Zack answers that he has no intention of telling her and asks back what will he do if he say he killed her. This enraged Danny who begins spouting his obsession for her eyes, but Zack dismisses this and reveals that Rachel wants him to kill her so Danny doesn't get to decide what's going to happen to her. Finding out Rachel is alive, Danny offers Zack some medicine that he has in exchange Zack gouge out Rachel's eyes and give it to him. In respond, Zack retracts his words of not interested in her eyes because her expression would be boring without them so Zack refuses Danny's offer.
As Danny leaves, Zack tries to pursue him, dragging himself from the hallway to the room, but Danny got away. When Rachel comes back but without medicine since Danny has taken them, she instead gives him the knife he asked her to bring. Zack reveals that he originally used knife as his weapon to kill. Zack then insists they continue their way, ignoring Rachel's objection. Along the way, they encounters snakes. As Zack is unable to use his scythe because it feels heavy due to his injuries, Zack tries to use his knife, but the snakes are too many. They eventually manages to barely escape from the snakes, but Zack lost his strength again from his injury. Rachel's concern for him, which she never does before, makes Zack questions if she's feeling guilty for something. When Rachel tries to brush off the subject by saying she'll go back to look for medicine for him, Zack tells her not to dodge the question and Rachel going alone would be the same as dying. Rachel defends her decision by reminding she has her gun, but Zack snatches the gun away from her and shows that the gun has no bullets.
Having enough, Zack points out that Rachel is contradicting herself as she wants him to kill her but yet she is also willing to die so save his life. He tells her not to do things half-heartedly and questions what she actually wants from him. Rachel finally admits that she has been wondering why she wants only him to kill her but could only think that the reason is because of the oath made to God. While Zack admits he did make the oath, he also believes that God doesn't exist in the world. Rachel is distressed by this but also said she doesn't want Zack to kill her just because he swore to God, but when Zack asks what is it, Rachel doesn't know either. Seeing Rachel is further in distress as she is confused with her own thoughts, Zack tells her to smile even if she's terrible at it. After seeing Rachel forces herself to smile, Zack collapses again. Knowing he is unable to stop Rachel, Zack lents her his knife for protection before falling asleep again.
Zack wakes up to find Rachel tending to his wound, stopping the bleeding and is ready to stitch it. Zack tries to insist that he'll stitch his own stomach, but reluctantly let Rachel do it after she finds out he can't stitch. Seeing Rachel's quite beat up condition, Zack asks how she got the medicine from Danny, but Rachel reveals that she got it from the reverend. He then asks why she went this far for him, insisting that Rachel answers his question when she once again tries to avoid it. Rachel answers that she did so because she has viewed Zack as her God, creeping him out but Zack decides to let her think that way for the time being. Once he has been tended and took enough rest, Zack and Rachel continues to the next floor, but not before visiting the church where Gray was.
Seeing the church without the said floor master present, Zack wonders how Rachel got the medicine from the reverend. Rachel says it wasn't easy and remarks that Gray has soft spot for Zack. The thought makes Zack vomit from disgust, telling Rachel not to say something like that again. They then proceeds into the elevator inside the room where Rachel got the medicine from. While going up, Rachel suddenly asks how Zack got his burn wounds. Zack was rather suspicious of Rachel's curiosity and warns her it won't be a good story, but Rachel doesn't mind with it. Zack tells her how his father tried to burn him and his mother to death, but he was resilient to the flames and his mother covered him with clothes. However, his mother then abandoned him at the illegal orphanage. Zack asks how Rachel thinks about his story, but Rachel simply replies that she's glad to know more about Zack. In return, Zack also thinks it's good for Rachel to know.
At floor B1, Zack discovers a room filled with fake flowers and stitched up corpses of a couple. After entering the room and sees everything, Rachel suddenly went panic and desperately asks Zack to kill her. Confused, Zack reminds her that he'll kill her only after they get out of the building. However, Rachel still asks him to kill her until she abruptly passed out. Hearing a sound coming from outside the room, Zack goes out only to find a toy. The moment he stepped out, Danny closes and locks the door with Rachel inside. Danny would only agree to let him in if he can learn more about Rachel and promises that he won't hurt her.
Not having any choice, Zack continues to explore the whole floor with Grey's help and finds a TV with a video. He watches the video that shows Rachel's counselling session with Danny. From the video, Zack learns that Rachel killed her father in self-defence after he killed her mother over Rachel's condition and then Rachel stitched her parents' corpses to make them her ideal parents. Zack breaks the TV and realizes that Rachel is in fact the master of floor B1. Now finding out the truth, Zack confronts Rachel and Danny back in the room where Rachel has regained consciousness, questioning the former if she will kill him because he is in her floor. Knowing Zack has found out everything about her and came into realization that Zack is not the God that she desires, Rachel tries to kill Zack, luring him into many traps inside the floor that she and Danny has set up when the latter brought her in.
After struggling and evading the many traps, Zack corners Rachel again in the first room, but he let his guard down, which allows Danny to hold him at gunpoint to the head from behind Zack while Rachel points her gun from the front. To Zack and Danny's shock, Rachel instead shoots Danny as she can't live with him and she wants to kill Zack herself. Before Rachel can shoot again, Zack pushes and holds her down. When Rachel starts to cry saying she doesn't want to die while being an abomination to her God, Zack silences her by reaffirming that the one who swore an oath to kill her was not her God, but him. He further rebukes her behaviour for running away and making excuses for her actions while he doesn't. He tells Rachel to look at him for who he truly is and swears the oath they originally made to only him while he will swears to only her. This helps Rachel come into terms with her actions and renew her oath with Zack.
While finding out the exit of the building is at B2, more precisely at Grey's church, they return to Rachel's room to pick up her handgun, but is surprised to find Danny once again has gone missing, meaning that he is still alive. To make it matters worse, Rachel's handgun has been disabled by Danny, rendering it unusable so they decide to continue their way out by breaking through the stained glass where they find a stair leading upstairs. Uneasy with Danny still alive, Zack suggests that they should find and kill him for good, but Rachel is against it since Danny knows the whole building more than they are, which will make it dangerous for them if they try to look for him. As Rachel is unarmed, Zack gives her his knife for self-protection until they get out of the building.
On their way up, however, the building begins to explode, causing fire and debris to block their path. Zack's fear of fire causes him to freeze on the spot until Rachel risks herself to get the flame out of the way so Zack can break through the falling debris. In the process, Zack finally overcomes his trauma against fire. They are barely able to reach the top of the stairs before it collapses at the cost of Zack's scythe being broken from the continuous breaking. Before going out, Rachel asks Zack if he truly wishes for her death because she wants her death to be desired, though just a moment ago Zack gave her his knife and thought she might have been being selfish. Zack replies that he gave her his knife so that she could stay alive until he kill her. He admits that up until now, he never had done something for anyone else, and he would never do something if he didn't desire it.
Feeling relieved by Zack's answer, Rachel and Zack are about to leave the building, but just only a few steps away, Rachel is critically shot by the wounded Danny who has been the one exploding the building in an attempt to stop them from escaping; even if it means killing himself as well. Zack tries to attack Danny, but gets shot as he is unarmed. Zack's attention quickly turns to the wounded Rachel who apologises to Zack for being unable to keep their promise. Zack desperately tells her not to die and make him a liar, but believing she won't survive, Rachel assures Zack he is a human being so there's no need for him to dedicate himself only to her as he has done enough by always being there for her. Before she loses consciousness, Rachel tells Zack that she will carry the burden of their oath herself so there's no need for him to think of himself as a liar. Distraught by Rachel's apparent death and regretting for not killing Danny earlier, Zack tries to use the last of his strength to kill Danny, who is immobilised by an arrow from Grey's crossbow. Grey interrupts that Zack should save his strength to escape the building, but Zack retorts there's no point of him escaping if Rachel dies. However, hearing that Rachel would be saved if she is taken outside, Zack carries Rachel and leaves the building before it burns down.
Outside, Zack once again tries to get Rachel to wake up. He then hears police sirens and soon the police cars arrive. Realising that the police are the answer to what Grey meant by saying Rachel would be saved, Zack allows himself to be arrested and let the police take the dying Rachel into protective custody to save her life. Before he lets himself be arrested however, Zack reaffirms to Rachel that he will keep his oath to kill her. After Zack is arrested, he is charged for the murder spree in recent years. Since he is found together with Rachel who went missing during her questioning, he is also charged with murder of Rachel's parents and kidnapping her despite Zack's denial, though he admits to the other killings. Based on these charges, Zack is sentenced to death penalty.
Not long after Zack's death sentence is decided and he is imprisoned, Zack escapes prison and breaks through Rachel's room at the rehab facility where she stayed after the incident at the building, shocking her as she asks how he got out of prison, to which Zack simply answers that he broke out Rachel then asks if he still wishes to kill her, something that Zack confirms. He then tells Rachel to go with him, questioning if she had forgotten their promise. Rachel tearfully answers that she will never forget because it's an oath between them. Just as the police arrive and start pushing the door; that Rachel has blocked, Rachel escapes with Zack through the window, once again pleading him to kill her. In respond, Zack tells her to stop crying and smile.
What happened to Zack and Rachel afterwards is left unknown as when the police finally managed to break into Rachel's room, the both of them were already gone, leaving only Zack's old knife and trails of blood from he broken window. In the novelization, the police immediately conduct a search for Zack and Rachel after the night they escaped together, though the the search is fruitless due to not having any single trace or clue of their whereabouts.
Zack and Rachel has a rather bad start. Zack tried to kill her after she stumbled in his floor and Rachel tried to escape from him out of fear. After Rachel lost her will to live, Zack lost interest in killing her, even got freaked out when she requested him to kill her like he originally intended to. Seeing Rachel's intelligence, Zack thought she could be useful for him to escape the building so he promised to kill her if she help him. Initially, Zack finds Rachel's lack of emotions boring, though he would listen enough to her instruction when the situation requires them to brainstorming, which shows how he trust her to be smart enough to help him. Zack is further annoyed by Rachel with the way she do things without question nor considering the consequence reminded him of how he was. However, Zack eventually started to get closer to Rachel as he realized that she views him as a human being for who he is instead of a monster, tool, or serial killer like other people does. He is determined not to die, yet he grows to care for Rachel and goes as far as risking himself to protect her on several occasions. Even though when Rachel tried to kill him Zack could have killed her to defend himself, Zack instead helped her to accept herself. The extent of his bond with Rachel became very deep after he convinced her to renew their oath and even refused to leave the building when he believed Rachel has died even though he previously said that he has no intention to die with her. While he at first only wanted to keep the promise between them because he has vowed to never lie, Zack begins to genuinely cherish the oath he made with Rachel not only for himself but also for Rachel's sake. He let himself be arrested by the police to save Rachel's life and then break out of prison all for the sake of fulfilling their oath.
Not much interactions between Zack and Eddie, but the two of them dislike each other, particularly in regards of who will be the one to kill Rachel. Eddie dislike Zack for destroying all of the gravestones he had made and getting in his way in getting closer to Rachel, even making his gravestone half-done than the rest of the gravestones he had made. His dislike for Zack intensified after Rachel chose Zack over him. Zack also takes quick dislike for Eddie and immediately tried to kill him, constantly calling him 'damn brat' and the sorts, especially after Eddie made it his goal to kill Rachel.
Out of all floor masters, Zack seems to hate Cathy the most. Zack takes instant hatred against Cathy for targeting him for her sadistic punishments and most of all for viewing him as her playthings that reminded him of how he was treated as a tool by his caretakers in the past. Throughout his obstacle in her floor, Zack set his goal to kill Cathy no matter what to make her pay, which he succeeded as he killed her without mercy. Cathy has sadistic obsession for Zack whom she regarded as her ideal sinner and takes delight in torturing him the most. For this reason, she constantly targeting him both physically and mentally throughout her floor, and thus is disappointed when she thought she couldn't kill him herself.
Zack and Danny have mutual dislike for each other. Initially, Zack didn't think much about Danny, but after growing close with Rachel, Zack came to dislike him due to the doctor's obsession for her eyes and was enraged when he thought Danny had killed Rachel, intending to kill him even if it means unable to get out of the building. Similarly, Danny didn't think much of Zack until he found out that Zack and Rachel were teaming up and learned that Rachel not only wants Zack to kill her but also viewed him as her God. This was further intensified after Rachel rejected to live with him despite all the things he has given her, but yet cherished her oath with Zack.
Gray is the one who brought Zack to the building as one of his "angels". The relationship between these two were not shown much. However, Gray shows more interest and attention to Zack than he does to other killers within the building due to Zack's nature who only knows to kill that makes Zack "pure" in his eyes to the point of calling the serial killer a "crystallize-winged being". His interest in Zack drives him to save the latter when he fell into one of the traps in B1 despite having broken the rule of the building, and later when Danny was about to kill Zack and Rachel. Zack, on the other hand, finds Gray irritating for his long-worded and cryptic ways of explaining things. And the thought of Gray having soft spot for him disgusted him.
- "Ohh... and if you die, then gimme a "I'm dead!" to let me know." – Episode One, to Rachel
- Zack's character is often compared to Garry's from the game Ib, another Indie horror game, in state of position-wise. Both characters are two grown men somewhere in their 20's assisting a young female protagonist (Ib for Garry, and Rachel for Zack) on trying to escape from a dangerous place, with that being the Building run by Abraham Gray and the World of Guertena.
- Zack doesn't know how to read, but he is shown able to recognize the shape of letters, as he recognized "B3" written on a document on B4 freezer and Rachel's name, later on.
- He has an surprisingly good stamina, as he has been shown to survive an electric chair torture for a long time, poisonous gas, etc. He has also been shot by a few bullets from a gun by Cathy and Danny.
- He has pyrophobia: the fear of fire, due to what happened to him when he was a child.
- It is speculated that he may have a type of Impulsive Control Disorder (ICD) which is a class of psychiatric disorders characterized by impulsivity – failure to resist a temptation, an urge, an impulse, or the inability to not speak on a thought.
- Zack is the most popular character in a questionnaire from monthly magazine Da Vinci published by Kadokawa Media Factory Brand in category "Characters other than Rachel that you like." 
- Zack seems to be smarter in the anime. In B1, he didn't eat the pizza, while in the game and novel, he eats it.