Ryoko Koiso (小磯良子?) Voiced by: Tomo Sakurai:The daughter of the Koiso-style kobujutsu karate master, initially set on fighting each and every high school delinquent, and convinced that Kitano is evil and very strong. After fighting him, however, she discovers his true nature, and little by little she becomes his girlfriend
- In the story, she is considered very strong, having only been beaten by sneak attacks or accidents. Both her and Shirataki Ikuno are observed of having the same personality traits.
- Her birthday is November 30th and Blood type is B.