During a summer break, junior high student Nagasumi Michishio heads to the Seto Inland Sea. While swimming at Mio Sun Beach, his leg cramps abruptly. No one nearby hears his frantic cries; he is pulled under and begins to drown. Just before he loses consciousness, a mermaid surfaces and pulls him to safety.
That evening, Nagasumi is visited by the woman who rescued him. She introduces herself as Sun Seto, a mermaid belonging to a yakuza clan. Under mermaid statutes, revealing a mermaid"s identity to a human warrants execution. To avert this grim fate, the Seto family offers Nagasumi a choice: marry Sun or be killed by Gouzaburou, the clan"s head and Sun"s father. With no other alternative, Nagasumi consents to wed her.
The newlyweds now must conceal their marriage. Their days are filled with secret meetings and hidden signals, while the ocean"s surface hides their true bond. They learn to blend into human society, adopting disguises and mastering new skills. Sun also possesses a rare gift that lets her communicate with sea creatures, which becomes vital as Gouzaburou"s relentless plots grow more dangerous. Amid bizarre schemes from various foes, a sincere, innocent affection grows between them as they navigate their clandestine life.
AIC 
Gonzo Digimation Japan