Nube and his classmates set out for a small island to indulge in some seaside fun, but their merrymaking is interrupted by a local resident's chilling account. According to the tale, there's a sea spider in the waters encircling the island that metamorphoses into a predator once it reaches the age of two centuries, preying on humans to sate its hunger. Unfazed by the warning, Yukime's inquisitiveness is piqued and she resolves to investigate the narrative. As soon as they arrive, a gorgeous girl emerges on the shore, beckoning Hiroshi's attention. Inevitably, eerie events start unfolding, with Kyoko and Ritsuko-sensei suffering vicious assaults. As doubts about the enigmatic girl's true identity mount, the sea creature legend becomes increasingly convincing.