Rika Kinugawa

Twenty-six-year-old Hiroto Suwa; his wife, Naho; and their old high school classmates—Takako Chino, Azusa Murasaka, and Saku Hagita—visit Mt. Koubou to view the cherry blossoms together. While watching the setting sun, they reminisce about Kakeru Naruse, their friend who died 10 years ago. Mourning for him, they decide to visit Kakeru's old home, where they learn the secret of his death from his grandmother.

One day, Naho Takamiya receives a letter written to herself from ten years in the future. As Naho reads on, the letter recites the exact events of the day, including the transfer of a new student into her class named Kakeru Naruse. The Naho from ten years later repeatedly states that she has many regrets, and she wants to fix these by making sure the Naho from the past can make the right decisions—especially regarding Kakeru. What's more shocking is that she discovers that ten years later, Kakeru will no longer be with them. Future Naho asks her to watch over him closely.