Rin Kagamine's childhood best friend, Shun Otonashi, transfers back to her middle school just as she's in the middle of puberty. Shun's demeanor has changed so much since they were young that Rin is confused as to how to talk to him. On the way home from his first day of school, Rin suddenly asks him why he's returned to the neighborhood. He answers, "I wanted to see you again, Rin," as a joke (?). At those words, Rin's heart begins to thunder...

(Source: Kadokawa)