Houtaro and his team receive information that the 102nd Chemy has unexpectedly appeared. Houtaro, Supana, and Sabimaru begin a search based on this information, and arrive at a certain research institute where Sabi's brother, Ken'ichi, works.

A new Malgam appears at the institute. Is the 102nd Chemy real after all? And behind it all is the resurrected Geryon!? Houtarou and Supana transform into Riders...!