Sixteen-year-old Takamiya Naho's world is upended when she receives a letter supposedly penned by her future self at twenty-seven. The letter forewarns her about the arrival of a transfer student, Naruse Kakeru, and urges her to watch over him closely. With the cryptic message in hand, Naho grapples with deciphering its significance not just for her own destiny but also for the enigmatic Kakeru's fate.