Hiroto Suwa visits a cherry-blossomed Koboyama together with his high school classmates, Takako Chino, Saku Hagita, Azusa Murasaka, and Naho Takamiya who Hiroto married and had a child with after the graduation.
Looking at the sunset from atop the mountain, they are thinking of Kakeru Naruse who passed away ten years ago. Kakeru Naruse was a transfer student who moved from Tokyo to Matsumoto city on the day of the second grader’s opening ceremony. Suwa immediately got along with Kakeru and realized that Kakeru and Naho were having special feelings for each other, but he pretended not to know anything about it. The winter of his seventeenth birthday, Kakeru suddenly died.
Ten years later, Suwa is in deep remorse after learning that Kakeru’s death was a suicide. ‘I’m such a terrible guy who deprived Kakeru of both Naho and his future. If only I was aware of these feelings at that time…’ Believing in a miracle, Suwa writes a letter to himself in the past.
The letter contained all the events that led to Kakeru’s death, his deep regrets as well as his true feelings at the age of 26. There is also a message given to himself in the past. The sixteen year old Suwa receives the letter and he will try to create a new future. There is also a new future for Naho and Kakeru and Suwa will be there to see them walk their new path.