Jero, known as "The Leopard" (or "Tiger Jero" in the Japanese anime), initially worked at his father's X-City mattress store before joining Team Shark Tooth. There, leader Gabu Samejima supplied him with a mountain bike featuring a hidden motor engine, which Jero refrained from activating in races. Gabu later seized remote control of the motorized bike without Jero's permission during a critical race against Sho Yamato. After losing to Sho, Jero abandoned Team Shark Tooth.

He then aligned with Team X, battling Sho Yamato in Idaten conflicts on Earth. Defeated by Sho a second time, Jero’s failure under Team X resulted in his forced return to the X-Zone dimension.