One day at the end of summer vacation, the monster buster agency receives a telephone call. "Many sea bathers go missing mysteriously. Please examine what is going on.". They get happy because they don't go anywhere during summer vacation. Mikoto, Takeru and Sui head for the isolated island to bust monsters. While staying on the island, they stay at a house of the head of the island. They enjoy sea bathing but while examining and busting monsters, they notice the presence of the big and strong monster behind the scene....