Hiroto Suwa, along with his wife Naho and their former high school companions Takako Chino, Azusa Murasaka, and Saku Hagita, embark on a journey to Mt. Koubou to admire the cherry blossoms. Amidst the beauty of nature, they reflect on their departed friend Kakeru Naruse, sparking a decision to delve into the secrets of his tragic past. Through a visit to Kakeru's ancestral home and a revelation from his grandmother, they uncover the truth behind his untimely demise. Overwhelmed by remorse, Suwa and the group opt to draft letters to their younger selves, aiming to bring solace to their hearts. Armed with insights from the future, the 16-year-old Suwa now holds the power to reshape destiny. As he stands at this pivotal juncture, what path will he choose, and what consequences will unfold in this altered reality?