Mao Ootori attends Otori Academy, an institution locked in a violent power struggle between the rival Kameyama and Otori families vying for dominance. Drawn into the escalating horrors plaguing the school, she is targeted by "Iron Mask," a mysterious assailant who sexually assaults students while masquerading as a demonic entity. During a confrontation, she resists the attacker but is overpowered until Hitomi Kameyama intervenes to save her.

As sinister rituals and factional tensions escalate, Mao joins efforts to expose the truth behind student disappearances and supernatural disturbances. She ventures into forbidden zones and allies with figures like Persia and April to counter threats such as the Fire Witch’s machinations and the exploitation of occult forces, actively working to dismantle the darkness consuming the academy.

Mao’s background, including familial connections, personal motivations, and history outside the conflicts, remains undefined in existing records.