A fourteen year old girl with sleepy-looking eyes and a large scarf that Shinkurō "saves". She is actually a reputable hitman from the Akuu Company known as "Guillotine". Though she is just fourteen, she unintentionally has perverted reactions to events, such as assuming Shinkurō wanted a threesome in the back alley with her and Murasaki. As if pressing his hand against her chest wasn't proof enough that she was a girl, she even offered to show him below. She seems to be weak to the cold and heat. After encountering Shinkurō a couple more times, she develops a crush on him and steals a kiss from him. Now, she is trying her best to understand the concept of friends as she slowly makes the effort to make other friends within their circle.

Even though she's an introvert, her personality dramatically changes whenever she wields any knife-type weapon in her hand. She appears to have supernatural strength, being able to carve pavement and metal railings into pieces with just one stroke using a butter knife. Much like Yūno Hōzuki, her family, Kirishima, is also part of the thirteen Inner Families, descendants of assassins. Her male name indicates she is the direct descendant of the head family.

Kirihiko appears in the OVAs of the anime adaptation.