Minato Wadatsumi, a fisherman's son, has lived in a port town for all 17 years of his life. Despite his background, he cannot swim, and he is scared of fish! After unwillingly throwing a stranded fish back into the sea, Minato is swamped by a wave that drags him down to its depths. Upon regaining his senses, he wakes up surrounded by cute mermaids in the deep-sea world of Latimeria. Claire, the Queen of the Deep Sea—also referred to as the Primo Mermaid—reveals that Minato has been chosen as Latimeria's prince. As the prince, he can turn a mermaid into the next queen through true love and a kiss. Although Minato has no wish to stay in the ocean, only the power of the Primo Mermaid can bring him back to the surface, forcing him to be the prince. After meeting Akari Irie, his caretaker, Minato believes that mermaids may be like any other girl. However, he quickly finds out that they can all transform into deep-sea fish! While many girls aim to become the succeeding Primo Mermaid, only Minato's phobia of fish prevents them from flooding him with their passionate love. [Written by MAL Rewrite]