Mizuno Kouichi (水野光一) was a classmate of Karin. He is 13 years old, and his birthday is May 1. He has green/blue hair and brown eyes. His blood type is B. He is 165 cm tall and weighs 52 kg.

Kouichi was a star player on the school soccer team, although he was only a first year student. He was liked by many girls, including Karin and Kaoru.

Kouichi was a big fan of Buurin.