The students learn that they are to choose a school activity and Tsukune is having a hard time choosing when he comes across the swimming club with Moka who is a bit reluctant to investigate because water has a purifying effect on vampires and drains their powers. The head of the swimming club, Tamao Ichinose, tries to isolate Tsukune for herself. After getting wet, Moka ran away. Tsukune soon realizes that the pool instructors are consisted of Mermaids and their intention was to eat the swimming club members. Tamao then attempts to eat him, just as Moka came back to stay with Tsukune. In an attempt to save Moka from drowning, Aono releases the Inner Moka, which teaches the mermaids the error of their ways. Afterward the inner Moka reprimands Tsukune for not understanding the other Moka.