Yui Kanzaki/World of If

In the alternate ending, World of If, Yui Kanzaki (神崎 優衣) is Shinji Kido & Ren Akiyama's accomplice who is aware of the existence of the Mirror World and the Rider Fight who becomes Alternative Zero (オルタナティブ・ゼロ).

World of If
After Shinji becomes Ryuga, he starts to rampage in the Mirror World. Hideyuki Kagawa, as Alternative Zero shows up with an army of twelve Alternatives in order to destroy Ryuga. As they prepare to attack Ryuga, Yui Kanzaki shows up. Kagawa laughs; Yui is the source of all their troubles and if she dies everything will end. They attack her instead, but Ryuga, having his sanity returned shields her. He reverts to Shinji and dies. Kagawa is shocked that there's a Kamen Rider who would give up their life for someone. Yui says she has a favor to ask of him.

With the Survive Card in his hand, Ouja, as the final Rider, stands before Odin. 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 hits 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. After Eri died, he quits being a Kamen Rider while throwing away Knight's Advent Deck. While wandering at the streets, a man shows up and gives him an Advent Deck and turned him into Odin's puppet.

With a full anger, he yells out 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 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 and dies as Shiro failed to grant her a new life and mourning her death.

Alternative Zero
Rider Statistics Rider Senses: Ability Parameters: Special Attacks:
 * Rider Height: 190 cm.
 * Rider Weight: 93 kg.
 * Eyesight: 20 km.
 * Hearing: 15 km.
 * Punching Power: 300 AP (15 t.)
 * Kicking Power: 450 AP (22.5 t.)
 * Maximum Jump Height: 50 m.
 * Maximum Running Speed: 100 m. per 4.5 sec.
 * Slash Dagger: 2000 AP (100 t.)
 * Accelerated Attacks: 2500 AP (125 t.)
 * Psycoroader: 4500 AP (225 t.)
 * Dead End: 8000 AP (400 t.)
 * Advent: Psycorogue: 6500 AP (325 t.)

In the S.I.C. Hero Saga, Yui became the Alternative Zero in order to confront Odin. The Alternative Deck gives her these following stats.

Contract Monster
The Alternatives' sole contract monster, Psycorogue, resembling a humanoid, Psycorogue could transform into a motorcycle called the Psycoroader. This contract monster has white armor with black accents while Alternative Zero and Alternative's armor were black with white accents, contrary to other Riders whose armor was similar with their contract monster. The Final Vent Dead End transforms Psycorogue into a motorcycle then Alternative and motorcycle spin-out faster and faster until they ram into the opponent.

Advent Cards
Unlike the other Advent Cards, Alternative and Alternative Zero's cards are different in appearance; the terminals and images are printed crosswise unlike the original Advent cards that have theirs printed lengthwise, and are given the title, "Alternative Advent Card Alchemy System" at the back. Also, there are green characters on the cards, which may give information to the Visor on what kind of card is swiped. Because their equipment was designed by themselves, the V-Buckles' and Card Decks' appearances were different from the other Riders.

Slash Visor: The card reader of Alternative Zero/Alternative was mounted on his right forearm. The visor voice was different from those of real Riders, the voice was female. Another difference was how the cards were used with the visor. The cards were swiped (similar to the Rouzers which would later be used in Kamen Rider Blade), which burned up with jet-black flame and disappeared when the card was vented.
 * Advent (AP: 6500): Summons Psycorogue.
 * Sword Vent (AP: 2000): Conjures a lance.
 * Accele Vent (AP: 2500): Increases Alternative's movement speed.
 * Wheel Vent (AP: 4500): Transforms Psycorogue into Psycoroader
 * Final Vent (AP: 8000): Executes Dead End. Psycorogue transforms into a motorcycle, then Alternative and motorcycle spin-out faster and faster until they ram into the opponent. Only Alternative Zero performed his Final Vent. Alternative was killed before performing it.

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
 * Slash Visor - Alternative Zero's Visor that enables him to use Advent Cards

Vehicles

 * Psycoroader - Serves as Alternative Zero's motorcycle