Watch Niji-iro Hotaru: Eien no Natsuyasumi [Sub: Eng]

The story revolves around a sixth-grade boy named Yuuta on his summer vacation. His father passed away one year ago in a traffic accident, and Yuuta now goes alone to visit a place where he and his father once shared memories. The two had gone often to an unused dam deep in the mountains to collect the rhinoceros beetles nearby. Yuuta suddenly receives a shock in a thunderstorm, loses his footing, and gets knocked out. When he wakes up, he sees a small girl and a village — except this village is the one that should be submerged below the dam. Yuuta realizes that he slipped back time to over thirty years ago, before the dam was completed. Another summer vacation, and another chance for Yuuta to reclaim what cannot be reclaimed, begins.