Nijiiro Hotaru: Eien no Natsuyasumi

Fuente: AniList

One year ago, Yūta lost his father in a car crash. Now in the 6th grade, Yūta goes to catch beetles in a dam near a mountain, a place he often went with his father. There, Yūta meets a strange old man, and while walking in heavy rainfall, slips and blacks out. When Yūta awakes, he sees a child, Saeko, who shows him a village from the past. A precious summer vacation for Yūta begins.