Jigoku Sensei Nube: Kyoufu no Natsu Yasumi! Asashi no Uni no Gensetsu

A group of students and their teacher, led by Nube, travel to a small island for a beach outing. There, they hear a warning from a local about a sea spider, a creature said to become a human-eating monster after 200 years. Yukime becomes intrigued by the legend. A mysterious girl appears on the beach, captivating Hiroshi. Soon after, Kyoko and Ritsuko-sensei are attacked under unusual conditions. The girl's true nature is called into question, and the legend appears to have some basis in reality.