Gynabalas is a man-beast type monster with long horns and blue black and white spots over his body who was commanded by Bosgan. Besides attacking with his horns, he also wields a sword in battle. Bosgun had invented a machine that turned people into humanoid animals (mostly pigs). When Gynabalas was sent to obtain a kid who was turned into a humanoid gorilla, he ended up in conflict with Kohtaro who became Kamen Rider Black RX, until the kid returned and attacked Gynabalas. Joe disguised himself as a humanoid pig version of Kohtaro to trick Bosgun, Gynabalas, and the Chaps into capturing him. When Kamen Rider Black RX arrived, Joe shed his disguise and Kamen Rider Black RX fought Gynabalas, destroying the machine that turned people into animals and returning the people to normal. Kamen Rider Black RX fought with Gynabalas until their fight leads outside of the factory. When Gynabalas managed to hit Kamen Rider with his sword, Kamen Rider called out his Revolcane to disarm Harmful Brass. When Gynabalas's sword was knocked away by Kamen Rider's Revolcane, he used his sword to slash into Harmful Brass's stomach destroying him.