In the spring, 16-year-old Takemia Naho receives a strange but detailed letter from an adult herself from a 10-year-old future. At first she thought that this was someone’s joke, but then the events mentioned in the letter, such as the appearance of a newcomer to the class, really have a place to be. Nearly two weeks after Kakeru returned to school, Naho finishes writing. In the letter, the 27-year-old Nakho informs the 16-year-old that she more than anything else regrets that Kakeru is no longer with them in the future, and asks her to take care of him.