Naho (voiced by Hanazawa Kana) is an ordinary second-year high school girl who lives a calm and ordinary life. One day, Naho received a mysterious letter from herself 10 years later. Naho 10 years later claimed that there was an irreparable regret in her life, and she sent this letter that traveled through time and space to make up for this regret. At first, Naho just regarded this letter as a prank, but the next day, the boy named Naruse Sho (voiced by Yamashita Seiichiro) mentioned in the letter actually transferred to Naho's class. According to the letter, Naho will fall in love with Sho, and Sho will die in the winter of the year when he is 17 years old. What can Naho do to avoid this tragedy?