Ever since Seine entered Tatsuya's life, things have definitely taken an interesting turn! But now their fight against the evil mermaids hits closer to home as Tatsuya's childhood friend, Nagisa, is infected with the parasite that will make him do the mermaid's bidding. To make things worse, Nagisa seems to be going after Seine. What can Tatsuya do to protect his friend? And when one of the evil mermaids who disguises as a cute girl transfers to the school, the danger level just cranks up a notch!