At the start of the game the Player can be killed by Yukari if they refuse to help her, since she already told them her plans. This is a non-standard joke ending, and the only time the Player is referenced in game.
Deciding he can't be witness to her crimes, Yukari reveals her plans and kills him when he runs to call the police. In the true route of the game, he reappears, injured, and attacks Yukari before she can kill the boyfriend. If Miho is still alive at this point she will come to Yukari's aid and protect her.
Miho makes a deal to lend Yukari a hand and not report her if she helps her deal with him. She explains that he has been stalking her, and if Yukari believes Miho, she confronts him in the hall and kills him if he fails to convince her that he is innocent.
The big gay is dead in the true route killed by yukari.
In two routes Miho will be killed, one of which sets the game up for a Bad Ending if Yukari decides Miho can't as trusted as she makes herself seem. This would later come back to bite Yukari when Tanaka attacks her and she has no-one to save her.
In another route Yukari is killed by Wakabayashi if he gets her to trust him, then he went on to reveal this to Miho and kill her.
He is killed in the true route of the game along with everyone else.
Tanaka has several deaths that can be triggered throughout the game. In one he is taken hostage by Akira and can be killed by Yukari, or if she spares him they flee to another Classroom, only for Akira to corner them and kill them both. One one of the Main Ending routes, if the Player messes up he will be killed alongside Yukari and Miho if they fail to defend her from Minami.
In another route not involving Yukari, Tohru gets angry and kidnaps him, revealing his feelings for him and his plan to cut his legs off to make sure he can't escape.
In the True Ending of the game it was revealed that Yukari killed him.
After she strikes to attack Yukari, Miho will defend her and Yukari takes advantage of this to kill her sister, apologizing for what its come to. In the True Route, Miho would be the one to kill her instead- setting up Yukari's sudden broken mentality and causing her to kill everyone else.
It is implied she is injured or killed when Tohru confronts her and Tanaka. In the True Route of the game she was killed after she kills Minami to protect Yukari.
In the Final section of the game, he can be killed alongside Miho and Tanaka if Yukari fails to avoid her sisters attack. It is also implied he was a victim in the True Ending route as well.