It was the Underworld King Germain and Gaelya who descended to earth from the Ouroboros world. Their target is Fuga, the father of Rinne, the most powerful alchemist. The Three Dark Kings, including Gigist, are closing in on Fuga. Houtaro, Rinne, and Supana rush to the scene and transform into Riders! They confront the Dark Kings to protect Fuga, but they are cornered by the unprecedentedly vicious power used by Germain and the others...!