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.
When Yadomi Jinta was a child, he was a central piece in a group of close friends. In time, however, these childhood friends drifted apart, and when they became high school students, they had long ceased to think of each other as friends. One of the friends from that group, Honma Meiko, now has a wish she asks Jinta to fulfil. The problem is, she can't remember what her wish is anymore.
A year has passed since Menma's ghostly return to the Super Peace Busters. Although the time they spent together during that summer was short, the five members reminisce about what happened as they each write a letter to their lost friend.
