Kanata no Kimi no Te

Yuudai, a student preparing for university entrance exams, returns to the town he spent his childhood summers in and unexpectedly reunites with Shun, the friend he used to always play with. A certain buried memory resurfaces to throw Yuudai off, and then suddenly a child appears and says something strange...?

(Source: Pixiv Comic, translated)

Note: Chapter count includes an extra.