Captivated by the tale of The Little Mermaid since childhood, a young man named Nagi visited the lonely island of Tsukumo. There, he encountered Umioto, a girl whose beauty evoked the very mermaid he long admired.

It is a quiet, beautiful island.
Yet beneath its tranquil surface, a strict "rule" lies ever-present, a rule that must never be broken.

She offered a gentle smile.
But deep within her eyes, something trembled...

Eventually, Nagi uncovered the secrets hidden within the island...and the cruel fate that has been thrust upon her.

"Even so... I want to be with you."

Is this love...or a taboo?
Does salvation or ruin await beyond their choice?

[Translated from Novelgame]