In a shocking twist (okay, maybe not so shocking...), Kimihito learns that he's been playing host to a princess! Mero the mermaid is actually the daughter of the king and queen of the sea, and now her royal mother is summoning her back home. Kimihito, along with the other monster girls living in his household, go to visit the mermaid queen in the hopes of changing her mind. Along the way, they uncover a tangled scheme that involves kidnapping, royal intrigue, tragedy, and, of course, naughty tentacles. If this intrepid group can manage to stay un-molested long enough to solve the mystery, they could transform the entire mermaid kingdom! But for once, Kimihito isn't the only one risking his life in the name of interspecies relations.