Mizuha belongs to the Oni, a group vilified as demons by humans due to their fearsome masks, though they are ordinary people displaced by nobles invading their homeland. Forced into conflict, she faces Jun Tendo, a time-traveling teen pivotal to ending the war, challenging his human-centric views by revealing the Oni’s history of exile and fight for survival. Determined to reclaim their land, she urges Jun to join their cause, offering a blend of resolve and reluctant respect for his neutrality.

Her pragmatism surfaces as she equips Jun with a gem and dagger that fuse into a sword vital for defeating Gen’un, the antagonist exploiting mind-controlled human forces. In the final clash, Mizuha’s tactical guidance proves critical, aiding Jun to dismantle Gen’un’s army and unite divided factions. While her loyalty to the Oni’s justice never wavers, her alliance with Jun marks a tactical evolution from adversary to reluctant ally, prioritizing survival over old grudges.

Rooted in her people’s oppression, Mizuha embodies their collective resilience, channeling generational trauma into a tempered resolve to mend human-Oni divides. Her arc focuses on navigating wartime diplomacy, though her personal history remains anchored to the broader struggle rather than individual ties beyond the conflict.