Nube gets a beach episode premise and immediately weaponizes it. A folklore setup that could have been filler instead becomes a genuine hunt for something that might actually be hunting back, with a teacher who can't just punch his way through an old man's warning. The sea spider legend sits there the whole time, real and patient, waiting for someone curious enough to confirm it exists.

Hell Teacher Nube arrives at a small island with his class for a summer beach trip. An old man living there tells them a grim legend: a sea spider lurks in the open waters nearby, and once it passes 200 years of age it becomes a monster that devours people. Curious, Yukime sets out to learn whether the tale is true. Then a mysterious girl suddenly appears on the beach. Her strange charm draws Hiroshi to her at once and overpowers him. Soon odd things begin happening to the others, and Kyoko and Ritsuko-sensei are attacked under unexplained circumstances. Questions grow about who the girl really is, and the old legend starts to look real after all. The film is an action story set during a summer vacation that turns frightening.