Ren Akiyama/World of If

In the alternate ending, World of If, Ren Akiyama (秋山 蓮) is one of the participants of the Rider Fight known as Kamen Rider Knight (仮面ライダーナイト). Following Eri Ogawa's death, Ren was manipulated to become Shiro Kanzaki's puppet and became Kamen Rider Odin (仮面ライダーオーディン).

World of If
In the World of If, after Eri Ogawa died in the hospital, Ren himself quits being a Kamen Rider while throwing away Knight's Advent Deck. While wandering at the streets, Shiro Kanzaki shows up and give him an Advent Deck and turned him into Odin's puppet. Ouja, as the final Rider, stands before Odin. His wish is for the Rider War to continue for all eternity. While in the middle of the battle, Alternative Zero jumps in and join forces with Ouja in order to fight Odin. Ouja activates his Final Vent; Venoviper transforms into a bike and charges at Odin, spitting poison along the way. A moment before it his him, though, he activates his Time Vent and vanishes, then reappears on Venoviper's seat, behind Ouja and strikes him quickly.

Right before he dies, Asakura sees Odin's face, through the hole in his helmet melted through by Venoviper's poison, revealing Ren's face. The mask completely crumbles away and Ren comes back to his senses. He looks down at his body and realized what happened. With a full anger, he yells by the name of Shiro Kanzaki as he appears and laughing in glee. Now that Odin is the victor of the Rider Battle, and now he can finally grant Yui a new life. Ren notices that the Alternative Zero and has a weird feeling about him as he heads over and yanks out the deck. Turns out it was Yui all along. She revealed that she borrowed it from Kagawa to stop Shiro, and reaches out to him. But he has no body, and can't grasp her hand. Yui faints while dies as Shiro failed to grant her a new life and mourning her death.

Equipment

 * Advent Deck - Transformation device and Advent Card holder
 * V-Buckle - Transformation belt
 * Advent Cards - Trinkets that enable a Rider to summon Contract Monsters, access equipment, and use special abilities
 * Dark Visor - Knight's Visor that enables him to use Advent Cards
 * Dark Visor-Zwei - Upgraded version of the Dark Visor used to transform into Knight Survive

Vehicles

 * Ride Shooter - Motorcycle used by any Rider to enter the Mirror World