Osamu "Mayu-Mayu" Mayuzumi

About

Mayuzumi is a high school Biology teacher who donates a lot of blood to prevent his "true" personality from coming out. If he goes more than a week without donating, he becomes short-fused, highly energetic and ill-tempered; otherwise, he is meek and doesn't stand out too much.

Mayuzumi has been friends with Yamada since high school, and occasionally uses his donor card to donate blood more often than is allowed.