Kai Mikawa, a handsome, rich, but agoraphobic merman of the killer whale variety, crashes his personal submarine into the PE hall and declares that Sun is his fiancé and he has come to rescue her from her kidnapper, Nagasumi, and offers Nagasumi an obscene amount of money to hand Sun over. Nagasumi angrily refuses and during their fight Kai is exposed to the outdoors rendering him unable to fight. Kai later transfers into Nagasumi and Sun's class and challenges Nagasumi to beat him at the sports festival for Sun's hand in marriage. Despite Kai winning a footrace both Sun and Lunar argue over Nagasumi and ignore Kai completely. During the last race that will determine who wins Sun's hand it starts raining and Kai transforms into his killer whale form and loses the race. His challenge against Nagasumi is declared a draw.