Tsukune and Moka are having a hard time choosing an extracurricular club to join until Tsukune, hoping to see Moka in a bikini, decides on joining the swimming club hosted by mermaids. Moka becomes jealous as she watches Tsukune being flirted with Tamao Ichinose, the head of the swimming club. However, what Tsukune does not know is that Moka has aquaphobia, since water drains her vampire powers due to its purifying effects. During a swim meet, Kurumu and Yukari, who joined the swimming club with Tsukune, try to garner the most attention through the events. As Tamao tries to isolate Tsukune for herself, he sees the other mermaids preying on the other male club members. Moka arrives to save him and jumps into the pool, electrocuting herself. As Kurumu and Yukari hold off the mermaids, Tsukune swims to the bottom of the pool and removes the rosary on Moka's neck. Moka's inner self emerges and, due to being weakened by the water, instead tricks Tamao into leaping out of the water so she can give her a good kick. Inner Moka then reprimands Tsukune for not understanding Outer Moka and for making her cry. The next day, Shizuka Nekonome, the homeroom teacher, recommends Tsukune, Moka, Kurumu, and Yukari join her Newspaper Club instead.