Dark Shinji

Kamen Rider Ryuga (仮面ライダーリュウガ, Kamen Raidā Ryūga?) is one of the fictional character and the main antagonist in the Kamen Rider Ryuki: Episode Final. He is one of the 13 Kamen Riders the story revolves around. His Rider appearance resembles Kamen Rider Ryuki, but with a black look ripped all over and is similar to Ryuki's Blank Form. Aside from a brief cameo in the TV Special 13 Riders, his only screen appearance was in the movie Episode: Final. He is portrayed by Takamasa Suga.

Fictional character biography
In the alternative continuity of Episode Final, Yui Kanzaki had already met and befriended Shinji Kido, Kamen Rider Ryuki, when they were still both very young. As a result, the young and lonely Yui subconsciously created a duplicate of Shinji in the imaginary Mirror World. Several years later, this Shinji clone would adopt the identity of Kamen Rider Ryuga and join the Rider battle in order to pursue his goal of becoming a real person in the real world.

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 Ouja could kill her. Ryuga himself had destroyed Genocider and turned Ohja into blank form. Femme then finished Blank Ouja off.

In terms of character, Ryuga was the exact opposite of his real world counterpart. 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. Near the end of movie, he met his own fate at the hands of his real world counterpart when, after a climatic showdown, the two Rider's Final Vents collided, Ryuki surviving while Ryuga perished.

13 Riders
In the 13 Riders special (alternate retelling), 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.

Forms
Like original Shinji Kido, Dark Shinji transforms into Kamen Rider Ryuga through his Advent Deck and his V-Buckle.

Contract Monster
Modeled after a Chinese dragon and Ryuga's Contract Monster, Dragblacker is referred as the Darkness.

Trivia

 * Ryuga's name can also means "Dragon Fang".
 * aside from personality, the other difference between Shinji and Ryuga is their appareance that is completely backward (like mirror reflection).
 * Ryuga is the only rider in Kamen Rider Ryuki that is a non-human, being a doppelganger of Shinji Kido that originated from mirror World.