Takatsu Yusuke used to Hikojima every summer as a boy till his grandparents passed away.

In five year's time he visits the island again in part to collect material on the mermaid legend for his movie club and in part to have a rest and reminiscent on the past days.

At the beach he meets a mysterious girl who seems to know Yusuke. She passes him a flower asking if he could remember her by looking at the flower. He still can't remember her. And the moment he raises a head, the girl is gone.

So started the journey to discover memories of the youth.

[From vndbreview]