Mion is the heir of the Sozonaki family, and is the leader of the Hinamizawa School club. As the oldest in the class, she is the Class Representative.

Mion is actually the younger twin, and she was therefore born with the name Shion. Mion and Shion intentionally switched places when they were young.

Mion acts boyish, energetic, and confident, often teasing her friends. She is a very cheerful and sociable girl who enjoys games.

Her spoken line: Sekai no doko darou to, kono nakamatachi ga ireba taikutsushinai ne!