The "Superpower Development Research Institute" was suddenly attacked by countless unknown life forms, and the institute was completely destroyed. In the chaos, the superpowers Xiao Lei (10 years old) and Sayaka (12 years old), who were originally being experimented on in the institute, took the opportunity to escape. A few months later, the attack by the unknown life forms appeared again, and this time the target was Sayaka. Upon hearing the news, Shoichi immediately transformed into the Masked Rider Jaw, and went to the rescue with G3-X. Suddenly, G4 appeared, and his appearance surprised everyone. Because two months ago, the blueprint of G4 was stolen. It has great power, but the people who wear it are often unable to withstand it and are fatal. Who stole G4 and made it? Where did the attack of the unknown life forms come from? The war between Kamen Rider Jaw, G3-X, G4 and unknown life forms is about to begin!!