There is the world where humans and monsters live together.

One day, a pirate, the main character, is washed off on the shore of small island... When he regains consciousness, there are two girls in front of him.

"Are you a pirate? Human? Train us to be great marine girls!"
"What...?"

He is totally confused, but he later learns that the island has a legend about special treasure. Like this, their training life starts...

[From ErogeShop]