When Nube and his class arrive at a small island to carry out beach activities, they heard a forbodding tale from an old man residing on the island. Legend has it that there is a creature known as the sea spider in the open seas around the island. When the creature is past 200 years old, it will turn into a monster and devour humans to satisfy its appetite. However, curiousity kills the cat and Yukime decides to pursue the authenticity of the legend. And then, a girl suddenly appears on the beach. Possessed with a strange charm, she immediately attracts Hiroshi's attention and overcomes him. Soon later, strange things start to happen to the others whereby Kyoko and Ritsuko-sensei got attacked under strange circumstances. The true identity behind the mysterious girl is questioned and the legend behind the sea creature seems to be true after all.
Cuando Nube y su clase llegan a una pequeña isla para realizar actividades en la playa, escucharon una historia de un anciano que residía en la isla. La leyenda dice que hay una criatura conocida como la araña de mar en los mares abiertos alrededor de la isla. Cuando la criatura tenga más de 200 años, se convertirá en un monstruo y devorará humanos para satisfacer su apetito.
