My Bride is a Mermaid

Nagasumi enjoys his first date with Sun at the Bon Festival. However, most stalls are operated by the Seto-Gumi. Later, Nagasumi soon finds out that Sun's legs revert into a tail when she is splashed with water and must protect her by drying her legs.

Sun and Nagasumi get to spend a whole day alone on a deserted island. However, this is a trap meant to eliminate Nagasumi, as the group's notorious assassin and longtime friend of Sun's, the "Spiral Shell" Maki, is after his life.

As a dutiful wife, Sun follows Nagasumi back to his house in the city, where she is to live with him and his parents. However, the first day back turns out to be quite hectic and eventful.

Sun and Nagasumi attend their first day of school. Sun's father and the gang have all become teachers at their junior-high school, and Nagasumi's friend Sarutobi falls in love with Sun. Nagasumi must survive constant attacks from his new "teachers".

Mawari notices Sun's fishtail and comes to the conclusion that Sun is a fish. She keeps trying to splash Sun with water in order to verify her theory, but Nagasumi protects Sun, while at the same time trying to save Mawari's life from the mermaid code of law.

Nagasumi runs into Lunar, a popstar idol; her mermaid form is accidentally revealed to him. In turn, Lunar plans on making Nagasumi her slave forever. He finds out she is a childhood friend and rival of Sun. Lunar soon makes a plan to settle the score with Sun once and for all.

The situation at school keeps escalating, and even Maki is hurt in the process. In order to avoid total war, Nagasumi comes up with a plan to settle everything in a singing competition between Sun and Lunar, with Nagasumi himself as the collateral.

Nagasumi's life only gets more hectic with the arrival of Kai Mikawa, a handsome, rich, but agoraphobic merman, who insists that Sun is his fiancé. Kai transfers to the school and challenges Nagasumi for Sun's hand in marriage during Sports Festival Day.

A strange, huge, practically invincible man, stalks Nagasumi and nothing can get in his way. Nagasumi tries to tell his friends, but initially no one believes him. Eventually Nagasumi runs into Kai and they both start running for their lives. This episode is a slight parody of Terminator 2: Judgment Day.

After Sun and Lunar go on a diet, Sun's father buys her all sorts of presents to help her out, including some special "mer-water" that energizes and gives strength. But many problems arise when Nagasumi drinks it by accident, not only giving him the powers of a merman, but also growing him to gigantic proportions.