Kotaro Takahashi

Is the main protagonist of the series and has the partner of Ai Kitazawa.

Appearance
Takahashi wears a school uniform and has short hair with glasses. He also wears the signature collar of those trapped in the building.

Personality
Takahashi seems to have high intelligence as he thinks of ways to escape as well as survive.

History
He is a high school student who was attacked on his way to school when brought to the building.

Plot
Takahashi wakes up to see Ai Kitazawa unconscious lying next to him. As she gains consciousness she immediately slaps him demanding who he was and where they were. Takahashi explains his situation which is similar to Kitazawa's having both been attacked by strange men. Afterwards, Takahashi looks at the phone he has which suddenly gives a command telling them to open the locker inside the room. As they do they find a box with a syringe and a photo of a man inside. The phone then commands them to inject the needle into that man. They question the phone which then tells them that the necklaces also have the same drug that is in the needle and that if they deem them "unnecessary" then they will activate the collars to get rid of them as they see fit. With that, it gives them two hours to inject the man. As time ticks by they slowly question themselves, however, Kitazawa takes the needle and leaves the room followed by Takahashi. As they make it through the hallway they see the man in the photo yelling for help. Kitazawa then tells Takahashi that she will distract the man while he injects him with the needle. While Takahashi tries to talk her out of it, she tells him how she doesn't want to die before giving him the needle and leaving. Takahashi lies and waits as Kitazawa distracts the man learning that his name is Touyama and that he has food and water. As Kitazawa is brought to Touyama's room he forces her onto the bed knowing that she was sent to kill him. However, he is stopped by Takahashi who tries to inject him but fails. As they squabble Kitazawa sees the needle she takes it and injects Touyama. After Touyama is injected Takahashi and Kitazawa witness the man melt. The phone then congratulates the two and tells them to put the body in the box that was holding the syringe and picture. After Takahashi puts the man in the box the phone tells him to bring it to the staff elevator where the box is taken and a new one brought up containing food and water. Takahashi is then seen washing his hands to get rid of the sensation of touching the melted body. He then sees that the old building still has power and running water and starts to wonder who this could be for. Unknowing to him he is being watched from the air vent.

After killing Touyama, Takahashi and Kitazawa spend their time walking around the building to find a sketch of its layout. While looking at the sketch, they notice an elevator which they discovered is broken down to their disappointment. Afterwards, he decides that they should rest so they find the best bed in the building which they both sleep on. Both still awake Kitazawa questions what they will do after killing Touyama as they can't go back to their regular lives. This makes Takahashi think about Touyama's melted body which makes him sick. He rushes to the bathroom where he vomits thinking about the body. A noise brings him out of his thoughts and he walks toward the elevator where he hears the noise. On his way to check it out he takes a metal chair to defend himself and quickly looks into the elevator only to see metal cans strung to the ceiling. Touching the cans he realizes it's a trap and turns around only to see a malnourished woman in her bra and underwear. The woman grabs him while getting ready to stab him with a syringe. However, before anything is done Kitazawa grabs the woman's attention and is seen holding a mop for protection. The woman is shocked at Kitazawa's presence wondering why she was there, but before anything is said Takahashi kicks the syringe out of her hand and onto the floor. Kitazawa races to get it before the woman who tackles her to the ground. Fortunately, Kitazawa manages to stab the woman resulting in the woman's death. The phone then congratulates them again and tells them to but the body in the box like what they did to Touyama. Angry Takahashi shouts to the cameras telling the ones doing this that he will find them.

Takahashi is seen putting the woman in a box as he contemplates the situation as well as noticing the woman had questioned Kitazawa. He then brings food and water they were given to Kitazawa as she's huddled in a corner. They agree to look around some more and as Takahashi turns around a boy is standing right in front of him which catches Takahashi and Kitazawa off guard. The boy doesn't seem surprised and introduces himself as Higashino. Higashino then brings a girl named Matsuya who is hidden behind a wall. Higashino then asked Takahashi for a smoke which he doesn't have which angers Higashino. Matsuya then asks Takahashi to help them escape which he considers but tells them that he and Kitazawa need rest which prompts the other two to leave allowing Kitazawa to ask what he thought of the two, which he can't answer at the moment. Seeing Kitazawa's crumbling resolve, he reminds her of what she said before and how both of them were going to stay alive. Afterwards, Takahashi is seen feigning sleep while eventually telling Higashino who is about to inject Takahashi with a syringe to stop as Kitazawa is seen holding Matsuya hostage with her own syringe. Takahashi tells Higashino to drop the syringe and explains how he knew this would happen as he and Kitazawa had already done it. Takahashi then asks them how much time they had and asked them if they want to die as the time runs out or help him escape. Kitazawa then releases what is actually a wire from Matsuya's neck. Takahashi then grabs Higashino and explains the plans as well as saying he knows the way to escape.

Takashi promises them both that they won't die however he tells them to stay in the room as he leaves with Kitazawa. Kitazawa questions him which he responds that he did not have a plan. He then tells her that they should look for more clues which leads them to the bathroom. Takashi helps Kitazawa reach one of the panels in the ceiling where a can falls. As he reaches the top he finds the area where the unknown woman stayed and takes the watch and map she left there. They both are then interrupted in their investigating as Matsuya confronts them with a mop telling them that she heard their earlier conversation. Kitazawa tells him to run which he hesitates to do but goes for it after she reassures him. Hearing someone in the hallways he runs to see rusted can food where he then notices the watch moving. Higashino appears behind him then demands the injector as Takashi tries to stall for more time. To his luck, he sees a butterfly which Hiashino explains its profile. With this he discovers a way out.