Kotoko is the leader of the "Fighter" class amongst the Warriors of Hope. The Warriors of Hope are a group of children who claim their goal is to rid Towa City of adults and then turn it into a "paradise for kids" as they envision it through a game they call Demon Hunting. 

Kotoko is a hot-headed girl who loves "adorbs" things.while Kotoko acts cheerful and happy most of the time she can actually be quite mean and cruel. 

Due to her trauma caused by sexual abuse, Kotoko triggers to the word "gentle" as the men who abused her had said they would be "gentle". When she hears this word, she becomes neurotic, and begins crying and screaming in fear, unable to calm herself down except when somebody tells her that they will not be gentle with her. it has left her so unhinged to the point that she takes a sick enjoyment in inflicting the same kind treatment that people had done to her upon what she refers to as "Cute Female Demons" prior to killing them. 

Kanon just happens to be on Her Kill List.