To protect the town of Kannai, the beautiful girl masked heroine Lucule lived peacefully with her father and older brother. But a new threat emerged among the monsters—a scheme in which the one who defeats Lucule would be granted dominion over Kannai. On her way home, Shiroto Shiori hears sudden screams and rushes to the scene, finding a monster attacking innocent civilians. Lucule ensures the bystanders escape safely, then dons her mask and transforms. After defeating the monster, the situation calms—yet on her way home, a new crisis strikes. Her father and brother have been brainwashed and capture Lucule. She transforms once more to fight back, but the monster evades her, and she is kidnapped. Surrounded by her brainwashed family, Lucule is overwhelmed as they lick and assault her body, driving her to climax.