Yonehiko Kitagawa

Two kids, Jim and Katy, finds an old map of an island where a pirate's treasure is hidden. They set sail to find the island but the pirates are also searching for the treasure. (imdb)

5000 years ago, evil demigod Poseidon and his minions attack the good mermen. A dolphin saves one of them, baby Triton. Later, as a young boy, Triton decides to avenge his family and end the reign of evil Poseidon and his monsters.

The ruler of the underground world is planning to conquer the whole world. Riding the fire dragon Isamu and Angel, the princess of the undersea kingdom, try to stop him from destroying their world.