Ganma is a plant-covered rock monster who wore an orange loin cloth. He can manipulate soil, split into rocks and launch the rocks on his body. His stone heart can allow him to regenerate from Black RX's attacks. Maribaron sent Ganma to battle RX as a diversion while she used a little girl to restore a key to the demon world for their invasion. When Kotaro was ambushed and pulled underground by Ganma, he became Kamen Rider Black RX and then became Bio Rider which allowed him to escape to the surface. He then reverted to Kamen Rider Black RX and fought Ganma before pulling back to find Maribaron. After the key was destroyed and RX thwarted Maribaron, she used Ganma to fight him. During the battle, RX discovered Ganma's stone heart and called out his Revolcane which he threw at Ganma's stone