Twenty-six-year-old Hiroto Suwa, his wife Naho, and their former high school classmates—Takako Chino, Azusa Murasaka, and Saku Hagita—go to Mt. Koubou to see the cherry blossoms together. As they watch the sunset, they recall Kakeru Naruse, a friend who passed away ten years prior. In mourning, they choose to visit Kakeru’s former residence, where his grandmother reveals the truth behind his death. Overcome with regret, Suwa and his friends resolve to write letters to their sixteen-year-old selves to find peace. Armed with the information from a letter sent by his future self, sixteen-year-old Suwa gets the opportunity to alter the future. What decisions will he make? What unfolds in this altered timeline?