Nishio Nishiki
Nishiki is Kaneki’s senior from Kamii University. In the past, his older sister was betrayed by her human boss and got turned in to CCG. He’s rather territorial, he doesn’t mind killing fellow ghouls who dare to kill in his hunting ground. In the beginning, Nishiki detests Kaneki whom he thought is trying to barge in his territory, but Kaneki manages to inflict serious wounds on Nishiki, which brings him to the brink of death.
Nishiki has a human girlfriend named Nishino Kimi. She finds him in an extreme state of hunger after his confrontation with Kaneki. Instead of fleeing in horror, Kimi proposes that Nishiki eat her. However, when Nishiki takes a bite of her, he stops, realizing that he doesn’t mind dying to save her. Nevertheless, it has left a bitemark on her arm.
Kaneki coincidentally finds Nishiki—still weak from the aftermath of their fight, beaten by other ghouls. He almost ignores him thinking that Nishiki “only gets what’s coming to him”, but finally decides to step in seeing they’ve gone too far. The ghouls flee in fear of the “half-ghoul from the 20th ward”.
Kimi, knowing about Kaneki’s identity as a ghoul, asks him for help to get food for Nishiki. However, she is kidnapped by Tsukiyama. Kaneki and Nishiki then fight Tsukiyama to rescue Kimi, and Touka helps them. Touka initially wants to kill Kimi because she is aware of their identities as ghouls, but in the end cannot bring herself to do it.
After the fight with Tsukiyama, Nishiki makes peace with Kaneki. He joins Anteiku, and provides help when they attempt to rescue Kaneki from the Aogiri tree.
Touka probably knows the nature of Nishiki’s relationship with Kimi, thus occasionally calling him “sex-obsessed”. Touka and Nishiki are often seen exchanging insults, but they’re actually friendly and supportive towards each other. Nishiki shares his work sheets when Touka is studying for entrance exam to Kamii University.
After the Anteiku raid, Nishiki gets separated from Kimi to keep her from getting involved with ghouls; while Kaneki disappears after being defeated by Arima. As they both share the same loneliness, Nishiki probably knows Touka’s feelings towards Kaneki more than everyone else. He supports her decision to wait for Kaneki. When Tsukiyama comes to :re and bombards her with all kinds of questions regarding Haise, Nishiki backs her up by telling him to stop pestering the Manager.
Nishiki is the first ghoul that triggers Haise’s memory of his past self. When he is overpowered by Kaneki, he takes off his mask and quotes himself from when Kaneki defeated him in the past. When he sees Nishiki's real face, Haise instantly recognizes him and calls his name unconsciously.
Nishiki: “I’ll die... I’ll die... Was it? No matter where you go, you’re helpless... Kaneki.”
Haise: “Nishio...senpai...?”
When Kaneki returns to :re after the Cochlea raid, Nishiki joins GOAT, and he becomes one of the people Kaneki trust the most. He even consults Nishiki regarding his health. When they are planning on the mission to take RC suppressant, Nishiki overhears Touka talking to Kaneki.
Touka: “Can we talk after you get back?”
Kaneki: “Sure.”
Nishiki: “Oh? Gonna propose or something?”
Touka: “Shut it, four-eyes.”
Nishiki knows Touka enough to predict her intention. While Touka isn’t really proposing to Kaneki like Nishiki thinks, he is clearly aware of her feelings; while Kaneki, on the other hand, is wondering if she’s going to hit him again. (I swear, this boy is really clueless.)
And when Touka asks him to get a burger—human food—he just puts two plus two together without asking questions, and concludes that whatever Touka talked about with Kaneki has proceeded even better than he expected. It is hinted that Nishiki tells everyone else that Kaneki and Touka are having a baby.