Having lost his parents, Morou Hiui lived with his grandfather, Dr. Shinzo, and his assistant. Other members of the family included a horse named Tenzan, a cat named Link, an armadillo named Armada, and a bat named Mirage. One night, they were attacked by monsters led by a man calling himself Original F! F claimed they were "Progressive Warriors" created by Hiui's father, and had kidnapped Dr. Shinzo to ensure their survival! During the battle against the Progressive Warriors, Hiui was severely injured. His life was in danger. Determined, Link fused with Hiui! It turned out the animals were actually Bio-Guarders, combat creatures created by the doctor specifically to fuse with Hiui! The battle to rescue the doctor began, with Hiui and the Bio-Guarders now in human form…!!