On a whim, Minato, a 20-year-old woman, finds herself dressing up in her friend's adorable high school uniform and briefly venturing out into the city. However, her day takes an unexpected turn when she runs into her stepbrother, Tooru, who happens to be only a few months younger than her. Throughout their school years, Minato has had to deal with constant jealousy and suspicion from other girls due to Tooru's good looks and reputation as a player.
To her surprise, Minato manages to convince Tooru that she is not actually his sister but someone who closely resembles her. As a result, Tooru begins pursuing a romantic relationship with Minato, and she reluctantly goes along with it for various reasons. What began as a harmless prank has turned into the most significant falsehood Minato has ever told!
