Kawasumi is a 15 year old student who attends Shuudai High. He is childhood friends with Ryosuke, and he is most attracted to the popular Suiren. Kawasumi is particularly talented in karate as he can easily defeat 3 attackers at the same time, and he was also the champion of a particular tournament (chapter 18).
Kawasumi was first seen as the only man who did not look Suiren's way. His first real encounter with her was when he saved her and her things from a senpai. Since then, the attraction between the two grew; Kawasumi would only talk to Suiren and Suiren, in return, would try her best to converse only towards him. By eating with each other on the rooftop, secretly going to the cultural festival together, and walking home with each other, their relationship developed.