The Mirror World version of Shinji Kido could survive indefinitely in his own universe without any extra protection, but could only stay in the real world for a short time before starting to disintegrate. Ryuga was occasionally mistaken for Ryuki. Ren had seen Ryuga attack Kamen Rider Femme while out fighting a Hydragoon, and thought Shinji had come to understand the meaning of the Rider War. He then demanded that Shinji fight him. Miho also mistook Ryuga as Shinji when Ryuga saved her before Kamen Rider Ohja could kill her. Ryuga himself had destroyed Genocider and turned Ohja into blank form. Femme then finished Blank Ohja off.
In terms of character, Ryuga was the exact opposite of his real world parallel. While the real Shinji was kind and innocent, the Mirror World version was cruel and scheming. He was responsible for the death of Kamen Rider Femme , mortally wounding her during their fight.In the 13 Riders special, Ryuga was among the Riders in the ending fight, only seen there. He and the remaining Riders activated their Final Vents on Shinji, then as Kamen Rider Knight Survive.
He uses his Black Drag Visor gauntlet on his left forearm to use Advent Cards from summoning his Drag Saber. His Final Vent is called the Dragon Rider Kick, jumping into the air to emit dark energy that paralyzes the opponent's legs and then deliver a flying side kick with Dragblacker flying behind to boost the attack's power with its dark flame.