Kouichi Mizuno, a first-year student at Sei Ringo Gakuen, captains the school soccer team and garners widespread admiration from female classmates, including protagonist Karin Kokubu and the shy Kaoru Hidaka, who frequently provides refreshments for the team. Despite this attention, he develops a romantic attraction to Tonde Burin, the superhero persona Karin adopts after transforming into a superpowered pig. Unaware of Karin's dual identity, he remains a dedicated fan of Tonde Burin. Kouichi navigates the complications of his unrequited feelings for Tonde Burin while overlooking Karin's own affection for him. Later in the series, he discovers Karin's secret alongside classmates. Though initially disappointed by the revelation, he ultimately accepts Karin as both herself and Tonde Burin, resolving the central romantic tension. His role centers on his school social standing, soccer team leadership, and inadvertent involvement in themes of hidden identities and youthful romance.