In life, everyone has griefs. Therefore, who would not grab the opportunity to transform the past if given the chance? Takamiya Naho, a sixteen-year old female, has her life abruptly thrown into flux upon receiving a puzzling letter which claims to be from her twenty-seven-year-old self. The letter informs her that Naruse Kakeru, a new transfer student, will be enrolling in the same class as her, and to keep an eye on him. What was the reason? She must resolve the letter’s mysterious warning for both Kakeru’s and her future.