After their father is transferred to another city, Yuuto and his non-blood-related step-sister Erica are left to live alone together. Despite Erica's harsh exterior and constant teasing, the two share a deep, hidden attraction. When a classmate's romantic pursuit of Erica forces their secret tension to the surface, the pair finally confess their mutual love and decide to start a secret relationship, pretending to dislike each other in public to keep their forbidden romance hidden from the world.
Yuuto's secret relationship with his stepsister Erica is complicated when his teacher, Miss Ichinose, discovers their affair and blackmails him into a sexual relationship of her own. As Yuuto navigates this dangerous double life, Erica eventually discovers his infidelity through photos taken by a classmate. This revelation sparks a fierce rivalry between Erica and Miss Ichinose, both of whom now compete for Yuuto's affection.