Ren Akiyama/Zi-O

In 2002, Ren Akiyama (秋山 蓮) was Kamen Rider Knight (仮面ライダーナイト). Seventeen years later, a new Rider Fight begins and Ren returns as Knight once more.

Advent Again
In 2019, a mysterious person restarted the Mirror World Battle Fight. On the fourth day, Ren was found by Takeshi Asakura. Takeshi, unlike the other participants who had no memory of the previous Rider War, told him that he remembered their past of killing each other which Ren replied that he (seemingly) remembered too.

Ren fought Ouja and was seemingly overwhelmed by him, as the latter got interrupted by a Mirror Monster. Goro Yura appeared as Zolda rescued Takeshi. After Ren had taken his leave, Kamen Rider Abyss ambushed  him for a short moment but  Ren quickly killed him with Hishouzan. It freaked Ren out as he has never killed anyone or has forgotten his fear of killing people. He let out a scream in horror and anguish.

On the fifth day of the battle, Ren transformed and joined the fray of the set up by Tezuka, rescuing a helpless Shinji from Asakura.

Another Alternative
As Zolda activated his Final Vent, Ren and the others all had to flee from the battle, causing a huge explosion as a result. Ren was later seen with Shinji in a parking lot. Ren knew Shinji's name, but Shinji mispronounced Ren's name as "Ron", just like in the past. The two wondered whether they had met before or not, with Ren not having any clue on the matter. Shinji thanked Ren for saving him earlier, but Ren stated that he did not save Shinji because they seemed to know each other. Instead, Ren remarked there was a voice in his head which kept telling him to stop this meaningless Rider War. Ren also admitted to Shinji that he had no memory about his past whatsoever. Shinji approved of Ren's motive, but Ren thought Shinji only wanted to stop the War because he was afraid of losing (Shinji had lost his Advent Deck). Shinji offered Ren a drink, only for the latter to spew the content on his face. Ren thought he and Shinji could not have been very close in the past. The two then decided to go and ask Asakura about the past.

Upon meeting Asakura, Ren stated that he did not believe in the mysterious woman's words. He said even if the winner was found, but none could get out of the Mirror World, then everything was meaningless. Asakura laughed and told Ren that their past was about fighting and killing each other, and that they had to continue fighting and killing for all eternity.

Some time later, an outraged Ouja was calling out Shinji and Ren, telling them to come and entertain him more. The two had retreated to an abandoned house. The mysterious woman appeared before them suddenly and declared that the time remaining was one day. Both Shinji and Ren were irritated, asking the woman why she was doing all this. The woman started to tell the two Riders her story: She was a woman named Sara. In the past, a man named Tatsuya Kano hit her with his car, putting her into the hospital. The man would then visit her frequently in the hospital, and the two started dating each other. However, the injury from the accident still did not allow her body to recover completely, and she was put back into the hospital again. Tatsuya, not wanting to lose her, became Another Ryuki and started killing countless people in the real world in hopes that the lives he killed would be able to resurrect her. Not wanting Tatsuya to kill more people, Sara's Mirror self restarted the Rider War. Because the real world Sara only had one day left to live, she said one day was the time remaining for the winner to be found.After Dark Shinji merged with Shinji and killed Jun, Ren and Kimura watched in horror and disbelief.

Alive A Life
Ryuga then attacked Kimura, wanting Kimura to die for him, saying that if he won the Rider War, he could escape to the real world and exist as a real being. Ren transformed into Kamen Rider Knight and used Trick Vent to distract Ryuga. Ryuga swiftly defeated the Trick Vent copies, only to find out Ren and Kimura had already escaped.

Ren was later seen riding his motorcycle, wanting nothing to do with the events anymore. However, he was surprise-attacked by three Mirror Monsters, regaining his memory upon being hit in the head by one of them. Finally realizing that it had been Shinji's voice that told him to stop the Rider War all along, Ren transformed and killed the monsters. Just as Ouja was fighting Ryuga, Knight intervened and said that Shinji was his opponent, not Ouja's. Ouja was amused, and began fighting Knight. Knight told Ouja that he was merely wanting to die, then used his Final Vent on him right after, fatally wounding Ouja, forcing him to flee.

Ren tried to make Shinji remember the past and come to his senses by revealing to him that the voice inside his head was Shinji's. Nevertheless, Dark Shinji stated it was useless to try and bring his real counterpart back, as he no longer existed. Ren shouted at him, telling Shinji to come back, otherwise he would have to kill Shinji. The two transformed and begin a duel, with Ryuga being the winner. As Ryuga was about to land the killing blow on Knight, the real Shinji began to surface and forced Ryuga to stop the attack. Ren said that Dark Shinji could never win because he would never understand the bond between him and the real Shinji. Knight then attacked Ryuga, forcing him back into human form. Ren, thinking that Shinji had returned to normal, de-transformed and came by his side. However, Dark Shinji was still in control of the body, he grabbed his Black Drag Saber and fought Ren in human form. Just as the two were struggling against each other, Asakura, also in human form, used his Veno Saber and interrupted their fight. Asakura prepared to stab Shinji with Veno Saber, only for Ren to shield his friend from the attack, getting mortally wounded as a result. It was at this point that Shinji finally regained his memory, as well as subdued his dark self for good.

As a dissatisfied Asakura disintegrated, Shinji came to his dying friend's side. Ren recounted the events of the past Rider War, saying that Shinji died before him at that time. Ren told Shinji to live this time. Shinji pleaded Ren not to die, but to no avail, as the wound he had received did not permit him to live any longer. Shinji revealed to Ren that Ren indeed was the man who kept appearing in his dreams since day one. Ren asked Shinji to come and check on his lover - Eri Ogawa - to see whether she was happy ot not. This makes Ren the second surviving and the tenth eliminated rider in the Rider Fight. In his last moments, Ren assured his friend that they would definitely meet again in a world without fighting and killing. He wanted to know if they could continue "annoying" each other once they got there like they used to do. A tearful Shinji agreed with Ren, just as the latter disintegrated in his arms.

Forms
Knight 1= 2= Rider Statistics Rider Senses: Ability Parameters: Special Attacks:
 * Rider Height: 195 cm.
 * Rider Weight: 95 kg.
 * Eyesight: 10 km.
 * Hearing: 25 km.
 * Punching Power: 200 AP (10 t.)
 * Kicking Power: 300 AP (15 t.)
 * Maximum Jump Height: 40 m.
 * Maximum Running Speed: 100 m. per 4.5 sec.
 * Wing Lancer: 2000 AP (100 t.)
 * Sonic Breaker: 1000 AP (50 t.)
 * Shadow Illusion: 1000 AP (50 t.)
 * Wing Wall: 3000 GP (150 t.)
 * Hishouzan: 5000 AP (250 t.)
 * Advent: Darkwing: 4000 AP (200 t.)

Ren can transform into Kamen Rider Knight's default form using his Advent Deck and V-Buckle upon forming a contract with Darkwing. His Visor, the Dark Visor, is a rapier that also functions as his personal weapon. In comparison to Ryuki, Knight has lower kicking power but higher jump height and running speed.

In addition to the Dark Visor, Knight can arm himself with the Wing Lancer (ウイングランサー), a lance derived from Darkwing's tail, by using his Sword Vent Advent Card. The remainder of Darkwing's body can be mounted on Knight's back, where its wings become a cape. This can be done by using either his Guard Vent or Final Vent. (However, Ren is often seen transforming into Knight with the cape already equipped). When using the Guard Vent card, the wings are in their original form and close around Knight to form the Wing Wall in order to protect him from attacks.

Using his Final Vent allows Knight to perform his finisher, the Hishouzan (飛翔斬), which equips him the Wing Lancer and Darkwing's cape form if he does not already possess them. Knight then jumps into the air and performs a drop kick while holding the Wing Lancer downward, resulting in it being parallel to his legs. Finally, Knight's cape forms a drill around him before he strikes the enemy.

Appearances: Kamen Rider Ryuki Special: 13 Riders

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
 * Darkraider Bike Mode - Serves as Knight Survive's bike.

Portrayal
Ren Akiyama is portrayed by Satoshi Matsuda (松田 悟志).

Appearances

 * Icon-ryuuki.png Kamen Rider Ryuki
 * Icon-ryuuki.png Rider Time: Kamen Rider Ryuki