Adult PC Game: Shoujo wa Manatsu ni Kaigan de by softhouse-seal Archive

Yuzuki and Shugo both worked at a beach house one summer vacation.
Yuzuki secretly yearned for Shugo and her heart was pounding at the chance, but then junior Aya appeared and took the summer in an unexpected direction...
a threesome of two girls and one guys.
How did this happen? It's all the fault of the hot summer sun...
Enjoy three lovers as they explore a dangerous relationship.