On the first day of her second year in high school, Naho Takamiya encounters a peculiar situation—a letter arrives addressed from herself a decade ahead. Initially doubtful, Naho soon realizes the authenticity of the message as events foretold start unfolding around her. The letter, penned by her older self, reveals a life colored by remorse and a plea for rectification. Warned to watch over the enigmatic transfer student, Kakeru Naruse, Naho faces a crucial task in altering a future where he is absent. Empowered by this epistolary guidance, Naho embarks on a mission to safeguard Kakeru from impending sorrow.