A man named Shouichi Tsugami has lost his memories. He doesn't know who he is, where he came from, or how he came upon his peculiar circumstances. Tsugami transforms into a powerful superhuman, Agito, whenever in the presence of the beings referred by the police as the Unknown, a race of powerful monsters. The Tokyo police have created a specialized unit to create their own Kamen Rider, the G3 Unit. Officer Makoto Hikawa dons the G3 armor and fights the Unknown alongside Agito. Can these two unravel the mystery of the Unknown and Shouichi's missing memories and origins?