Shinichi Ogasawara went to his relatives' house, whom he hadn't seen for ten years to spend his summer vacation.
Finding himself in a completely remote countryside, he lost his way under the blinding brightness of sun. But suddenly a girl appeared before him, sulking for no reason. She turned out to be his male cousin, Rio Ogasawara, a person who had been in very friendly terms with Shinichi. While overcoming his perplexity at how much Rio changed all these time, he promised to reignite the intimacy between the two through pleasure of the flesh, as it was in the past.

[Adapted from game description in Fanza]