Ryuga is a Mirror World copy of Shinji Kido created after Yui Kanzaki met Shinji. Due to her connection to the Mirror World, her imagination and memories of Shinji created Dark Shinji.
Due to his roots in the Mirror World, Ryuga could stay in the Mirror World indefinitely, but could only stay in the normal world for a limited amount of time, or risk death; the opposite of a regular Advent Rider.
Due to the multiple times the timeline was altered due to Kamen Rider Odin's Time Vent, not much is known about Ryuga during the Rider War. In the final version of the Rider War, Ryuga wasn't very active, and likely lived on in the Mirror World after the final Time Vent until the Mirror World was unsealed again.
Ryuga was sighted after a large scale battle, watching the combatants from the windows. He later made an appearance in the real world, destroying a city to gain Ryuki's attention so he could absorb him, only to be stopped and killed by the Last Dragonborn, Dragblacker's soul being devoured in the process.
Ryuga and Dragblacker (the latter's soul being restored in the process) later returned due to a "time glitch", and fought FoxMask. The two fought, but the fight ended with Ryuga's heart being ripped out. FoxMask proposed a deal with the dying Ryuga that would allow him to exist in the normal world if he served as FoxMask's shinkigami, and the Dark Rider accepted, and had his wound undone by time powers.
While he does serve FoxMask, Ryuga is more nominal than anything. Calling him good would be a massive stretch, given he is sadistic and scheming, and is considered the opposite of his regular world counterpart in terms of personality. His main reason for serving FoxMask is to exist in the regular world, and most of his good acts from thereon out were due to him simply following orders.
- Enhanced physical ability, to the point of outclassing Ryuki's base form; became even stronger as a shinkigami
- Advent Cards
- Advent (Summons Dragblacker)
- Strike Vent (Summons his own version of the Drag Claw, which he can use in conjunction with Dragblacker for the Drag Claw Fire attack, a stream of black fire)
- Guard Vent (Summons his own version of the Drag Shields, which serve as shields or large shoulder pads)
- Sword Vent (Summons his own version of the Drag Saber)
- Final Vent: Dragon Rider Kick (Ryuga floats into the air, paralyzing the foe's legs, as Dragblacker coils around him, followed by the latter firing off a black fireball at his master, launching him for a devastating flying kick attack)