Maki George, the younger brother of the leader of Nemesis, a secret organization bent on world domination, betrays his brother and the organization for justice. Nemesis uses human-monster hybrids for their operations. George steals an Injel, a magical creature that can transform humans, though it carries risks: men can lose their sanity and women without special compatibility become puppets of Nemesis.

George seeks a compatible girl to use the Injel and fight Nemesis. Guided by the Injel, he arrives at St. Eijo Girls' Academy, hoping to find such a girl but fearing he will drag an innocent into danger. When Nemesis attacks the academy, George uses the Injel to protect the girls but nearly loses control. Yuuki Hikaru, a student, transforms with the Injel, revealing her compatibility and defeating the monster.

George explains to Hikaru that the monsters are linked to a series of abductions and assaults at the academy, targeting girls compatible with the Injel. Angered by her friend's victimization, Hikaru decides to fight as a magical girl. George, with nowhere to go, is taken in by Hikaru and her mother, Yuuki Asuka, starting their cohabitation and battle against Nemesis.

[Translated from the official site]