Naho Takamiya, a shy high school student in Nagano, receives a letter from her 26-year-old future self detailing everything that will happen during her second year, including the arrival of transfer student Kakeru Naruse, with whom she will fall in love. The letter's most urgent warning: Kakeru will not be alive by winter. Guided by her future self's regrets, Naho and her close friends Suwa, Hagita, Chino, and Azusa try to change the course of events and keep Kakeru alive.