Geiz Myokoin

"I'm going to kill him."

- Geiz's declaration to kill Sougo Tokiwa in order to change the future.

Geiz Myoukouin (明光院 ゲイツ), alternatively spelt Gates Myoukouin , is a warrior from the year 2068 who transforms into Kamen Rider Geiz (仮面ライダーゲイツ) , the secondary rider of Kamen Rider Zi-O.

In an alternative future different from his own, he will be known as Geiz Revive (ゲイツリバイブ), the Savior of the World.

History
Geiz comes from 50 years in the future where he fought as a resistance fighter against the evil tyranny of the demonic king, Oma Zi-O. After Oma Zi-O kills many of the resistance fighters, he decides to travel back in time to kill Oma Zi-O before he can become the king destined to enslave the future, much to Tsukuyomi's ire. Tsukuyomi later discreetly follows Geiz.

Traveling to the Past
Using his personal Time Mazine, Geiz manages to find the possible identity of Oma Zi-O, in the form of Sougo Tokiwa. Geiz spent no time trying to chase the young man. However, he was intervened by the timely arrival of Tsukuyomi, who saved Sougo. Geiz then chases them to both the Prehistoric & Edo era, although he lost track of them after Tsukuyomi's Time Mazine accidentally ejects Sougo to the World of Build in 2017.

Geiz later finds Sougo once again, this time already transformed into Zi-O. After he berates Tsukuyomi for her failure in changing history, he proceeds to ask why did Sougo transform into Zi-O. Sougo replied that it was probably his fate since he was born, in which Geiz was somewhat reminded of Oma Zi-O's declaration of his tyranny. Deeming Sougo as irredeemable, Geiz transforms into Kamen Rider Geiz Ghost Armor, and addresses Sougo as Oma Zi-O before lunging at him.

Zi-O obtaining Build's Power
Geiz proceeds to summon four parka ghosts (Ore, Musashi, Edison, and Newton) to attack Zi-O. Geiz then attacks Zi-O relentlessly and proclaim that while Sougo had done nothing wrong in the present, Geiz will kill him for the sake of a brighter future. Geiz then attempts to kill Zi-O using Omega Time Burst, though Tsukuyomi intervened using her Time Mazine. After Tsukuyomi tells Zi-O to run away, Zi-O proceeds to summon his Ride Striker and flee from the scene. Geiz then summons his own Ride Striker to chase Zi-O. However, Geiz lost Zi-O track after a lengthy bike chase. Geiz then cancels his transformation and angrily questions Tsukuyomi for her motive in helping Zi-O. After Tsukuyomi replied that she didn't know either, Geiz orders Tsukuyomi to not interfere with his quest to kill Zi-O.

Geiz and Tsukuyomi later continue their search for Sougo when they notice Another Build appearing once again, even though Zi-O had defeated him before. Another Build then absorbs an nearly athlete into a Fullbottle, and Geiz deduced that the Time Jackers had also appeared in this era. Geiz decides to leave it be and focus on the mission. However, Tsukuyomi stops him as Another Build is about to absorb another athlete. Left without another choice, Geiz proceeds to transform and battle the Another Rider, to no avail.

Just before Another Build could deliver a finishing blow to both Geiz and Tsukuyomi, Zi-O appeared and counter the attack using the Zikan Girade and proceed to ask them if they are okay, much to both Geiz and Tsukuyomi's shock. Tsukuyomi starts to doubt whether Sougo is really Oma Zi-O or not as Zi-O manages to defeat Another Build, while Geiz is also rendered speechless for Sougo's sincere actions. However, Another Build somehow respawned again, to the trio's shock. As Zi-O deduces that only the real Kamen Rider Build could defeat Another Build permanently, he quickly goes to nascita, while Geiz vents his frustration to Another Build, and manages to defeat him. However, the Another Rider respawns once more.

Geiz proceeds to defeat Another Build again, for the Another Rider to respawn yet again. Geiz's transformation is then cancelled due to exhaustion. Just then, Sougo appeared while holding the Build and Cross-Z Ridewatches. Sougo gives the Cross-Z Ridewatch to Geiz and tells him that they must go to 2017 and defeat Another Build permanently using their newly acquired Ridewatches. They then travel back to 2017 using their Time Mazines.

Sougo and Geiz manage to arrive at the very scene in 2017, only to be interrupted by Heure of the Time Jackers. After Sougo and Uhr exchanged their arguments about the Another Rider, Uhr left the scene. The two Riders then transform and join up with Build and Cross-Z to take down Another Build. However, the change of events in the timeline has caused Build's and Cross-Z's powers to disappear, seemingly transferred into the Cross-Z and Build Ridewatches. Woz later appeared and tells Zi-O that using the Build Ridewatch will make Zi-O able to defeat Another Build, but Sento's memories as Build will be gone. Zi-O steels his resolve and transformed into Zi-O BuildArmor. Woz then joyfully remarks this moment. Zi-O Build Armor is now able to damage the monster, with Geiz subduing him with his Zikan Zax in Yumi Mode. Zi-O uses Vortex Time Break to finish the monster with Geiz utilizing the Zax's finisher equipped with the Cross-Z Ridewatch. As a result of their actions, Another Build does disappear for good, but Sento, now christening himself as Takumi Katsuragi, completely forgets about Sougo as the latter gives two blank Ridewatches for Takumi and Ryuga to safekeep. Geiz demands to know what's with the sudden anomalies in the timeline, but Sougo himself is confused about it as well, only exclaiming that Sento and Ryuga will choose to become Kamen Rider Build and Cross-Z in the future.

The next day, both Tsukuyomi and Geiz decide to rent Junichiro's spare room. Tsukuyomi explains that Sougo’s actions make them reaching an agreement to keep an eye on him. Geiz himself says despite Sougo's sincere actions, his vendetta towards him hasn't ceased.

Personality
Currently, not much known about Geiz, except for the fact that he is one of the rebellion fighters against Oma Zi-O who lost the fight and he lost someone close to him that died fighting Oma Zi-O, which shaped his vengeful personality. He is incredibly stealthy, as shown when he was able to easily sneak up on Sougo using the Time Mazine, not being noticed until the last minute by Tsukuyomi. Geiz is also incredibly determined to kill Sougo and he is highly paranoid towards the latter, as he is the one believed to be Oma Zi-O's true identity in the future.

Although somewhat baffled with Sougo's kind actions towards him and Tsukuyomi, Geiz discreetly declares that his vendetta isn't fading away. He is stubborn and often wants to resolve problems on his own, but has softened a bit to the idea of Zi-O helping him stop various Another Riders despite their tense relations. Still, this hasn't ceased Geiz's hostility towards Sougo, which worsens when the latter manages to defeat him single-handedly while under the facade of working for Kuroto Dan, with him becoming even more determined to kill Sougo. After the fall of Another Gaim, he directly declares to Sougo that he'll be more than ready to kill him anywhere and anytime, in the event Sougo embarks the path of becoming Oma Zi-O.

Despite his vows to kill Sougo, Geiz is still extremely conflicted due to being unable to see Sougo actually become Oma Zi-O. Because of this, he later on sincerely pleads with Sougo to throw away his Ziku Driver, to prevent Oma Zi-O to rise to power, and so he doesn't have to kill him. After Sougo has Geiz destroy his Ziku Driver, it is Geiz later on that gets him to fight once more, reminding him of the former's vow to become a good demon king. He also changes his vow to instead become a promise to stop Sougo from going the wrong path and end up becoming the demon king he is terrified of.

Power & Abilities

 * Stealth Proficiency: Geiz is able to discreetly follow a target or arrive where said target will appear without notice.
 * German Language Interpretation: Geiz has knowledge of German language as seen when he read Emu's note of the bug of the Another Ex Aid's gate to come inside the game.
 * Genius-Level Intellect: At the very least, his use of BuildArmor and his finisher, Vortex Time Burst, indicate that Geiz is proficient in equation and scientific formulae.

Forms
Like Zi-O, Geiz transforms by inserting the Geiz Ridewatch into the right-hand side of the Ziku-Driver and rotating the Driver 360 degrees. He accesses Rider Armor (ライダーアーマー) forms based on previous Kamen Riders by inserting Ridewatches into the left-hand side of the Ziku-Driver.

Devices

 * Ziku-Driver - Transformation device
 * Ridewatches - Transformation trinkets
 * Ridewatch Holder - A strap to carry Ridewatches
 * Faizphone X - Communication device

Weapons
Handheld weapons:
 * Zikan Zax - Geiz's personal weapon
 * Zikan Zaclaw - Geiz Revive's personal weapon
 * Faizphone X - Upgraded version of the SB-555P Faiz Phone wielded by FaizArmor

Suit-equipped weapons:
 * Shift Speed Speeds - Autonomous attack units provided by DriveArmor
 * Faiz Shot Shot - FaizArmor's replica of the SB-555C Faiz Shot accessed using the Faizphone X
 * Faiz Pointer Pointer - FaizArmor's replica of the SB-555L Faiz Pointer accessed using the Faizphone X
 * Drill Crusher Crusher - BuildArmor's personal weapon based on the Drill Crusher

Vehicles

 * Ride Striker
 * Time Mazine

Portrayal
Geiz Myoukouin is portrayed by Gaku Oshida (押田 岳). As Kamen Rider Geiz, his suit actor is Yuya Nawata (縄田 雄哉), whose previous suit acting role was that of Kamen Rider Build in the previous series' finale. Geiz is the first Secondary Rider since Zeronos not to have either Eitoku and/or Jun Watanabe as his suit actor.

Etymology
"Geiz" is a German word which means "stinginess" or "miserliness". However, according to Woz, Geiz actually means "King" (王) in their series as a counterpart to "Zi-O". It is a pun on English word "Gates" since in Japanese and Ancient Egyptian culture, and  both having "gate" etymologies: "a gate connects god and human" or "a gate connects humanity and future". The reason why using "Gates" instead of "Gate" is because of Toei staff's superstition. . It is later implied another reason for his name being "Gates" instead of "Gate" is due to the already existing use of the word Gate back in Kamen Rider Wizard.