Amid growing fear and chaos in the city, Seimi Shino, a beautiful girl beloved by everyone, obtains a magical compact after helping a mysterious old man on her way to school. The old man is actually a god who, witnessing the collapse of earthly order, chooses the pure-hearted Shino as his divine agent and tasks her with fighting to protect the city's peace. Meanwhile, the school janitor who always kindly watches over Shino drinks a strange, unsettling medicine recommended by a science teacher, causing him to undergo a terrifying transformation. He attacks Shino, forcing her to transform into Magical Mask and battle him—only to collapse from her own attacks. But when Shino approaches him with concern, the janitor suddenly lunges and bites down on her arm. Amid conflict and deep bonds, the story ultimately reaches a hopeful conclusion.