Sougo Tokiwa

Sougo Tokiwa (常磐ソウゴ) is a 18-year-old high school student who dreams of becoming a king one day. When Tsukuyomi and Woz travel to his time from 50 years in the future, he learns that he is destined to become the tyrannical ruler of their time, Oma Zi-O. With this knowledge, he makes it his goal to be a great king through kindness by becoming Kamen Rider Zi-O (仮面ライダージオウ). However, he faces Geiz Myoukouin, a Kamen Rider from the future who is bent on killing him to change the course of history.

History
Sougo Tokiwa was born on April 28, 2000. Living with his grand-uncle Junichiro in a clock shop, he attended high school at Hikarigamori High School, excelling in history but poor in physics. From an early age, Sougo believed that he would become a king, much to the consternation of his uncle and his friends chagrin.

The Birth of Zi-O
One day, Sougo found a mysterious watch-like item that was on the seat of his bicycle, and after examining the blank item, Sougo laid down the blank item, then went on home while minding his own. Later while bicycling down a small street up towards a stairway, a man in hood, holding a grimoire appeared out of nowhere, who told him that it would be a momentous day for him and to avoid the "red robot" before mysteriously disappearing.

He does indeed encounter the robot shortly after, run by a man in red and black attire and attacks Sougo. He is saved by a woman claiming to be from the future named Tsukuyomi in her Time Mazine. They seemingly travel back in time to 1671 Japan where she proves her legitimacy to him. Tsukuyomi warns Sougo that the watch he currently had possessed a tremendous amount of power and using it will make Sougo turn into the worst and lowest overlord, Oma Zi-O. Just before Sougo could reply, a fight occurs and Tsukuyomi decide to test whether Sougo is really Oma Zi-O or not by forcefully putting Sougo in the middle of the fight. The citizens proceed to throw Sougo to a river and doing so makes peace for themselves. Instead of lamenting his misfortune, Sougo is relieved to see that the group had reconciled, much to the citizens’ amusement. However, a red Kamen Rider, Geiz manages to tail them and the two retreat back into the Time Mazine.

When Tsukuyomi was being attacked by Geiz, Sougo gets kicked out of the mech and wakes up in a strange world with a huge wall in the horizon. As he ponders over this, a Smash attacked him but luckily Kamen Riders Build and Cross-Z appears to help. After revealing their names, Sento and Ryuga bring Sougo to the cafe Nascita.

As Ryuga drinks from a carton of milk, Sougo sees the expiration date and realized that he's indeed in the year 2017. Sento affirms that Sougo is indeed from the future since, after some analysis, Sougo's Ridewatch is different from any current technology. Before Sento can ask about the future, Tsukuyomi appeared and shot the three of them into unconsciousness using Faiz Phone X, in order to prevent Sougo from interfering with the past any more than necessary. He wakes up in his old home, believing it to be all a dream. Later, he encounters a monster with the similar look of Kamen Rider Build attacking civilians. He tries to stop him but is quickly subdued twice.

Sougo was approached by the prophet, Woz once again, who then tells him that he'll become an overlord who will reign over the future. Tsukuyomi desperately tries to warns Sougo to not use the Ridewatch. However, after some quick thought, Sougo decided to not become a tyrant, but to become a beloved overlord of the future, much to both Tsukuyomi and Woz’s surprise. After that, the blank Ridewatch revealed itself to becoming the Zi-O Ridewatch, then Sougo is given the Ziku-Driver by Woz to transform and battle the elusive Kaijin Rider. As it is his new beginning of becoming a Kamen Rider, Woz announced the introduction of Sougo as he was now Kamen Rider Zi-O, the King of Time, much to Tsukuyomi’s disappointment.

He is able to go on par with Another Build and is quick to defeat him using the Zikan GiLade finisher. Geiz enters the fray, seemingly frustrated with Sougo on his decision and Tsukuyomi as she failed in convincing him. Geiz proceeds to ask why Sougo became Zi-O, which the latter replied that it was probably decided from the moment he was born. Reminiscing Oma Zi-O’s declaration, Geiz deems Sougo as irredeemable and transforms using both Geiz and Ghost Ridewatchs to become Kamen Rider Geiz GhostArmor and advances towards Zi-O.

Obtaining the Power of Build
Geiz proceeds to attack Zi-O relentlessly until Tsukiyomi piloting the Time Mazine and tells Zi-O to run. After a lenghty bike chase, he manages to do so. Sougo then encounters Woz once more, who formally introduces himself. He states that the two that hail from the future are trying to change the future. Woz then warns him a group named the Time Jackers who have the same goal but to have another king of their choosing in the future. He claims to be the one keeping the timeline the same and that he's on Sougo side, remarking that his conquest has only just begun. He later finds Another Build fighting Geiz and rescues the two. With his Time Break, Zi-O seemingly defeats the monster once more, only to find it again within seconds. Believing the real Build could defeat him, he rushes off to find him.

Later, Sougo went to the same cafe to meet Sento and Ryuga again. However, due of Another Build's appearances, Nascita's scenery had changed, the fridge that was the passway to the Build laboratory is gone and both Sento and Ryuga become Lynks Band fanboys instead, seemingly forgetting their memories of being Kamen Riders and their encounter with Sougo the previous year. After Geiz destroy Another Build once again, Sento and Ryuga memories returned, and two blank-ridewatches that they somehow possessed turns into Build and Cross-Z Ridewatches. Sento then said to Sougo to take care of his past self and gives him the Build and Cross-Z Ridewatches. Although he doesn't understand at first, he quickly realizes that Another Build showed up and attacked Sento and Ryuga in 2017 and Sougo went back in time to help defeat it. He meets up again with Geiz and Tsukuyomi informing them and the two Riders head to their Time Mazines and head back to the past.

Sougo and Geiz manage to arrive at the very scene, only to be interrupted by Uhr of the Time Jackers. He tells Sougo that the host of Another Build's fate was to have his athletic career abruptly ended in an accident and that he helped him move forward. The latter argues that despite his ability to time travel and intervene with other's lives, it's that individual that can determine his or her future. Impressed with his statement, Wool wonders what his future will look like and walks away. The two Riders 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 to have transferred into the Cross-Z and Build Ridewatches. Zi-O uses the Build Ridewatch to become Zi-O BuildArmor, with Woz appearing and remarking this moment. Zi-O Build Armor 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. Remembering that Sento and Ryuga gave Sougo the Ridewatches, he asks the two to hold on to two blank Ridewatches for safe keeping. Sento corrects him by saying that his real name is Takumi Katsuragi, and he seems forget about Sougo. Geiz demands to know what's with 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.

Sougo wakes up the next morning to find out that Tsukuyomi and Geiz have rented out that his uncle's spare rooms. Tsukuyomi explains that him saving the two has questioned whether or not he will grow to become a vile dictator and have decided to keep an eye on him, with Geiz later saying his vendetta towards him hasn't ceased. Despite all this, Sougo seems to be fine with the two living under the same roof as him.

Obtaining the power of Ex-Aid
The first day of Geiz and Tsukuyomi took a class with Sougo, Sougo didn't feel relax a bit because whatever he did, they would follow and sneak on him, especially Geiz took a look at him closely when he was about to use the toilet. During the lunchtime, he hid inside the sport warehouse and met a student played a game from GENM Corp, similar to Mighty Action X game. However, when Sougo tricked the gym teacher for covering the student to play the game in quiet, Another Ex-Aid appeared and attacked the player. Sougo transformed and fought it, but after he got thrown, Another Ex-Aid disappeared. Geiz and Tsukuyomi came to Sougo and explained that it wasn't his fault and Another Rider had appeared.

At home, Sougo thought to play the game to lure Another Ex-Aid, but his skill was beyond help as he couldn't reach the level where the student would be attacked. Tsukuyomi said about if only there was a gamer which could help as even she and Geiz couldn't play any old video game, Sougo rushly caught an idea to search a gamer and went to search for Genius Gamer M after Tsukuyomi took a look on her history tablet. Sougo late to realize if doing things like running around to search for him was 100% a difficult task but as he got tired after he had done that. But he found another victim and Another Ex-Aid escaped in a blink, making Sougo couldn't even reach for it. Woz came and told Sougo to take the victim to the doctor.

Sougo, Geiz, and Tsukuyomi took the victim to Seito hospital. There, Sougo heard of a doctor who played game with the name Emu and asked where he was. Hiiro met them and asked about the ruckus and Sougo told him of what he wanted. Hiiro recalled about Emu was missing after he played the mentioned game after Sougo revealed that the incident of the disease was related to the game. There was a note and Hiiro as he claimed that he somehow could trust them, on playing the game. The note was written in German language and Geiz able to read it, revealing that it was a code for the player when they played the game. Sougo realized the meaning of the code after Geiz translated it and played the game, making them to be dragged to the game world itself and encountered Another Ex-Aid.

Sougo and Geiz transformed and battled against Another Ex-Aid. Another Ex-Aid was proven too strong to be dealt until they utilize Geiz Drive Armor and Zi-Oh Build Armor to overcome the odd and defeated it. Emu appeared and praised them that they solved the code in cold tone, transformed into Ex-Aid and attacked both riders afterward

Personality
Sougo is described as an ambitious young man who desires to be a king. However, upon learning of his future self being a tyrant, he decides to change his fate. The current reason is yet to be known of why he is like that except the fact that Sougo somehow felt that it is his fate.

Despite his grand ambitions, Sougo is a peaceful and genuinely kind man at heart, and will gladly take physical harm if it means stopping a conflict, much to Tsukuyomi’s confusion.

Sougo seems to have a verbal tic by adding "Feels like it" (気がする) in the end of most his sentences, mostly due of his optimistic approaches.

Power & Abilities
Skill:
 * Vast Historical Knowledge: According to Tsukuyomi, Sougo excels in history.

Weakness:
 * Poor Academic Knowledge: According to Tsukuyomi, Sougo was helpless in science. This was proven when he used the Build Armor, and instead of proper equations, it simply listed sentences stating that he 'didn't know' or 'something I learned in grade school'.
 * ​Game: Sougo lacks skill in video games.

Forms
Kamen Rider Zi-O transforms by inserting the Zi-O 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 Heisei Kamen Riders by inserting Ridewatches into the left-hand side of the Ziku-Driver.

Devices

 * Ziku-Driver - Transformation device
 * Ridewatches - Transformation trinkets

Weapons
Handheld weapons:
 * Zikan Girade - Zi-O's personal weapon
 * Ride HeiSaber - Zi-O's personal weapon while using DecadeArmor

Suit-equipped weapons:
 * Drill Crusher Crusher - BuildArmor's personal weapon based on the Drill Crusher
 * Unidentified Gashacon Breaker-like gauntlets - Ex-AidArmor's personal weapon

Vehicles

 * Ride Striker
 * Time Mazine

Relationships

 * Tsukuyomi:
 * Geiz Myoukouin/Kamen Rider Geiz: Geiz strongly believes Sougo is Oma Zi-O and is absolutely determined to kill him before he could become Oma Zi-O to prevent the future where Sougo supposedly becomes the tyrant that rules all with an iron fist. He refuses to call Sougo by his real name and cruelly refers to him as Oma Zi-O.
 * Woz:
 * Junichiro Tokiwa:

Past Kamen Riders:

 * Sento Kiryu/Kamen Rider Build:
 * Ryuga Banjo/Kamen Rider Cross-Z:
 * Emu Hojo/Kamen Rider Ex-Aid
 * Hiiro Kagami/Kamen Rider Brave

Portrayal
Sougo Tokiwa is portrayed by So Okuno (奥野 壮). As Kamen Rider Zi-O, his suit actor is Seiji Takaiwa (高岩 成二).

Rider No.
As the leading rider protagonist of Kamen Rider Zi-O, Zi-O is labelled Kamen Rider #35 (仮面ライダー35号) and Heisei Rider #20 (平成ライダー20号).

Etymology
Sougo Tokiwa's name is play on, the place where Shotaro Ishinomori lived and started his manga career during 1956 to 1961. "Tokiwa" also carries the word Toki (とき), which can be translated into time when it is written in kanji "時".

"Zi" in Zi-O's name could mean either time (時) or character (字), representing his "watch" and "Katakana" motifs while the "O" means king (王). It is a pun on English word "Zero".