Blue Lagoon ~Minami no Umi no Manan~

Agi Island is located northeast of the Philippines. The Protagonist Ryoutarou is a young shoemaker who lives peacefully on Agi Island. However, on the night of the next day a ship sinking accident occurred near the island, and on the coast he met a naked girl named Manan who was wrapped in a blue aura. And around the same time, a mysterious unit searching for her (Manan) landed on Agi island.

[Translated from DLsite Pro]