A blue-eyed merman named Nize rescues Prince Leonhart from drowning. Now the two are stranded on an island, seemingly alone, apart from mysterious voices which call to Nize at night.

Nize learns that if he stays too long on land with Leonhart, he will eventually lose his tail. To return to the sea and live together with other merfolk should be the obvious choice, but Nize finds his heart torn.