A long-necked turtle monster. He can bite, launch his head and neck out to constrict enemies, and shoot sparks from his mouth. He is commanded by Bosgun. Gynagingam put Reiko in the Hospital and had Utako give a message to Kotaro instructing him to meet him somewhere. When Kotaro arrived at the designated location, Gynagingam attacked him. Kotaro transformed into Kamen Rider Black RX and fought Gynagingam until Bosgun arrived. He transformed into RoboRider, but Bosgun revealed his new sword which was able to penetrate his RoboRider form, a few strikes from which caused Kotaro to revert to RX form. Kamen Rider Black RX called his Acrobatter and then retreated. When Shigeru and Hitomi were captured by Bosgun, Gynagingam, and the Chaps, a weakened Kotaro fought Bosgun and Gynagingam while Joe freed Shigeru and Hitomi. After Joe was wounded by Bosgun, Kotaro transformed into Bio Rider and fought them. Bio Rider was caught by Gynagingam and turned into water to escape and evade Bosgan's sword. After being disarmed, Bosgun retreated. Gynagingam was beheaded by Bio Rider who reverted to Kamen Rider Black RX and destroyed him with the Revolcane.