|“||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)
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 seemingly much quieter and reserved. He was shown to never say a word throughout the manga specifically.
Zack's real name is revealed to be Isaac Foster, according to a record of notes Rachel found containing information about both her and Zack. Soon, Rachel asked Zack about the story behind his burns, to which he answered that when he was born, his father burned him alive, but he was resilient at that moment. Fortunately, his mother wrapped him with clothes, however, Zack remembered that his mother left him behind only to toss him some money as well as his father.
He stayed in a 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, and with this Zack would 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.
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 was in love with. 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 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 while continuing his killing spree. After making his third kill, Zack was found by an old man who took the boy to his house and kindly fed 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 then, Zack stayed at the old man's house and everyday ate the bread given by the old man who picked it specifically for him. One day, the old man used the money he had saved to buy a better bread for Zack while praying for the boy's happiness. Unfortunately, on his way back, he was confronted by a young man. With the old man unusually late coming back, Zack went out to look for him, only to find him being killed. In retaliation, Zack killed the old man's murderer.
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. He later found her near the elevator, 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 sapping 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, Zack tried to kill Eddie but failed because of Eddie's control in the light source of the floor, 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. 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 accidentally sits on electric chair 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. 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, Zack decided to inject both syringes into himself.
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 fully allows Zack to regain himself. Not wanting to kill Rachel or got killed by Cathy, Zack resorts to cut his own stomach 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 hidden gun. With her guard down, Zack stands up and cut off Cathy's arm that is holding the controller before she could shoot Rachel, allowing Zack to kill her.
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 or 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 for him. He tells her not to do things half-heartedly and questions what she actually wants. 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. With 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 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 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. Rachel answers that she did so because she has viewed Zack as her God, creeping him out. Once he has been tended and took enough rest, Zack and Rachel continues to the next floor, but not before visiting the church where Grey was.
At 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. 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 she doesn't want to die while being an abomination to her God, Zack silences her by reaffirming that he is not a God and 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 coming into terms with her actions and renews her oath with Zack.
While finding out that 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 worse, Rachel's handgun has been disabled by Danny, rendering it unusable so they decides to continue their way out by breaking through he stained glass where they finds a stair leading upstairs. 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 froze in his 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 barely able to reach the top of the stairs before it collapses at the cost of Zack's scythe 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 a just a moment ago Zack gave her his knife and thought she might 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 done something for anyone else, and he would never done something if he doesn'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 attempt to stop them from escaping even if it means killing him as well. Zack tries to attack Danny, but got shot as well as he is unarmed. Zack's attention quickly turns to the wounded Rachel who apologize to Zack for 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, Zack tries to use the last of his strength to kill Danny, who is immobilize by an arrow from Grey's crossbow, in revenge. 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 the police sirens and soon the police cars arrives. Realising that the police is the answer of what Grey meant that Rachel would be saved, Zack allows himself to be arrested and let the police to take the dying Rachel into protective custody to save her life. Before he let 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 the recent years. Since he is found together with Rachel who went missing during the questioning, he is also charged with murder of Rachel's parents and kidnapped her despite Zack's denial, though he admits of the other killings he have done. 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 she got out from prison, to which Zack simply answers that prison is made to be broken out. Rachel then asks if he still wishes to kill her, something that Zack confirms. He then tells Rachel to come with him, questioning if she has forgotten their promise. Rachel tearfully answers that she never forgot because it's an oath between them. Just as the police arrives and starts 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.
Rachel Gardner: 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 and her constant reminder of their promise 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. Even though he is determined not to die, he grows to care for Rachel and goes as far as risking himself to protect her. 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. 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.
Eddie: Zack knows little about him, but he seems to dislike him since he wants to be the one who killed Rachel. Eddie has always questioned why Rachel choose Zack over him. In fact, Eddie is one of the two of which Zack calls a "freak".
Cathy: Zack doesn't know much about her, but he does somewhat disgusts and later hates her for her desire to "punish" him. Cathy is the other "freak" that Zack mentions when Rachel asks him about the floor guardians.
Danny: They really have a strong dislike for each other. Both of them would have killed the opposite if the wounds on their body did not stop them. They are rivals.
Gray: The relationship between these two were not shown much. However, Gray shows a great fond of Zack, calling him "a pure serial killer" or his "angel" and claiming that Zack is a "crystallize-winged being". Gray is the one who brought him to this building.
- "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."