One unfortunare evening, while you were staying at your aunt's home by the sea in Japan, you decided to relax on a floating matress on the water surface.

You were swept far away from the shore, when you fell asleep and rolled over to the sea. You faintly remember something dragging you away in the water... Now, you're laying on a sandy shore in a cavern. And from the water a creature you've only knows from myths is looking at you with cold expression and guarding the only underwater exit.