After a catastrophe destroyed their continent, the inhabitants of Mu adapted to living in the ocean in cities covered by huge domes. After many years in the ocean, the inhabitants began to possess psychic powers.

During an annual battle held to determine who is the best Mu psychic, Osper, a boy with a strong sense of justice, battles Drome, an older, brutish boy who is vengeful and evil. Osper wins the battle, though after Drome is defeated, he destroys the dome in revenge and escapes to Earth. Osper is sent to chase Drome and avenge his people. Above ground, Osper meets the International Crusader Police, who aid Osper in hunting down Drome to stop him once and for all.