Bioman 2 Maskman Saison 0

Commander Sugata discovered the existence of the Royal Underground Empire Tube, a malignant force that desires to dominate the land, which is based underneath Japan. He recruits five young people, each one specializing in a style of martial arts, and teaches them in the ways of the mystical "Aura Power" energy. A year after he recruited and trained the Maskmen, Tube is ready to strike.

Takeru fights to rescue a mermaid living in an underground pool being used by Igam to cause massive earthquakes to the surface.