Mahiro Oyama

Mahiro Oyama is the protagonist of Onimai, a withdrawn adult man transformed into a middle school-aged girl by a drug created by his scientist sister Mihari. The change forces Mahiro back into social life and everyday responsibility.

Mahiro Oyama after Mihari's experiment

Lazy, anxious, and accustomed to isolation, Mahiro initially wants to return to the old body. Friendships and school experiences gradually make the new life feel less threatening and more emotionally rewarding.

A changed body, school life, and recovery from isolation

Mahiro has no supernatural combat ability; the transformation changes age and sex while Mihari monitors the treatment. Relationships with Mihari, Kaede, Momiji, Asahi, and Miyo drive a story about rehabilitation, identity, and renewed connection.