Tsukuyomi (Zi-O)

"Tsukuyomi" (ツクヨミ) is a member of the Resistance who arrived in 2018 with Black Woz and Geiz Myokoin to guide Sougo Tokiwa into becoming a good king. She is also the younger sister of Swartz, but doesn't remember at first due to suffering amnesia.

History
Tsukuyomi is an amnesiac and has no memory of her past, other than a vision of her eight-year-old self alongside her older brother. Her current name is merely a code name given to her by the Resistance when she joined them.

In 2068, Oma Zi-O was being attacked by the resistance, which he managed to defeat with minimal effort. After declaring that no one will be able to beat him, Oma Zi-O clenched his fist and killed almost all of the Resistance members, save for Tsukuyomi as she was pushed to a narrow rift by the leader of the Resistance. She then decided to follow Geiz to 2018 to observe Sougo.

The Birth of Zi-O and Another Build
Traveling back to 2018, Tsukuyomi saves Sougo from Geiz and proceeds to show him his future in 50 years, becoming the most evil and despised demonic king in all of history. Despite her attempts however, she is unable to prevent Sougo from attaining the power of Zi-O and is hesitent to trust him, but after watching him, doesn't completely believe he will become Oma Zi-O, something her friend Geiz disagrees with as he proceeds to transform into Kamen Rider Geiz Ghost Armor to destroy Sougo.

Just as Geiz is about to finish off Sougo, she interferes with her Time Mazine and proceeds to take Sogou back to 2018 where they find Another Build is still alive and attacking people. Eventually, she and Geiz are cornered and Sougo saves them, explaining to them that they need to go back to 2017 and destroy Another Build. They travel back and Tsukuyomi watches from the sidelines and Sougo attains the power of the Build Ride Watch and he and Geiz destroy Another Build. Afterwards, she and Geiz decide to live with Sougo at 9-to-5 and monitor Sougo as he gains more power, ready to stop him the day he becomes Oma Zi-O.

Emu Hojo & Another Ex-Aid
Sometime after the Another Build incident, Tsukuyomi and Geiz enroll in Sougo's school to monitor him closely at all times. It's during this observation that a mysterious illness breaks out and the only clue to it is a handheld game that everyone seems to had before becoming unconscious. They eventually conclude that they need to find the Genius Gamer M for help which lead them to Seito University Hospital where they meet Hiiro Kagami and learn that Emu, the one they are looking for, has been missing for a while and the only clue to his whereabouts are a handheld game console and a note written in German. After cracking the code, the team of Sougo, Geiz, and herself are transported to another world where they confront Another Ex-Aid and meet Emu Hojo, Genius Gamer M, and Kamen Rider Ex-Aid. During the confrontation, they learn that Another Riders take the existance of the original Rider away, leaving the latter with no memories of their previous adventures, but still need to deal with the situation. Sougo eventually figures out what Another Ex-Aid, Ida, is after and he and she tries to help Emu by convincing him to stop attacking innocent people to save his son. However, he is too far gone and the only recourse is to destroy Another Ex-Aid's power. Emu gives Sogou the Ex-Aid Ride Watch and watches as Sougo leaves to take care of the situation. Afterwards, everyone returns to 9-to-5 and Tsukuyomi and Geiz are told by Sougo that he trusts them and their judgement and hope to get along.

Amanogawa High School, Another Fourze & Another Faiz
Tsukuyomi and Geiz start looking into another incident involving the dissappearance of school girls that are 18 years old and Libras. Their search brings them to Amanogawa High School, where Gentaro Kisaragi, aka Kamen Rider Fourze, attended school. Despite Geiz's insistance of keeping Sougo out of the situation, Tsukuyomi gets him involved and the three start questioning the students. During that time, Another Fourze makes his appearance as Sogou and Geiz try to defeat him but fail to do so. They are then taken in by the school's Kamen Rider Club and meet its advisor, Chuta Ohsugi, who notices Geiz's Ridewatches and gives Sougo the Fourze Ridewatch saying that Gentaro wanted him to have it. After that, Tsukuyomi does some digging elsewhere, learning about a young girl involved in the last attack on her friends, Karin Yamabuki, and eventually finds her in an abandoned building. She confronts her, trying to get answers when Masato Kusaka and Takumi Inui burst in, causing them to lose sight of her.

Eventually, Tsukuyomi and Geiz learn that Karin has been kept alive by the powers of Another Fourze finding and hunting down 18 year old Libra girls and also learn that Sakuma has been doing this for over 15 years, which explained why he was able to become Another Faiz as well. Eventually, the groups confront Sakuma and Karin and learn of their connection to Masato, being they were from the same private school, and proceed to find and defeat both Sakumas to stop him and her from hurting each other anymore.

Back to 2009 & Learning the Truth
Since Geiz was hesitating to destroy Sougo and prevent the rise of Oma Zi-O, Tsukuyomi started to do a bit more digging into Sougo's past and learned that his desire to become king started after a tragic bus accident. Wanting to learn more, she went back to 2009 and saw Sougo prattling on about becoming a king and saving everyone. She also gets a glimpse of Another Zi-O, Hiryu Kakogawa (but thinks nothing of it). She goes back to the day of the accident and learns a shocking truth about the whole incident: The one who caused the accident and lives of both Sougo and Hiryu's parents was none other than Swartz. She attempted to save Sougo by shooting at Swartz but he blocked the shot, causing it to hit near Hiryu and knocking him unconscious. Swartz then transports all of the kids off the bus and leaves the adults to die in a horrible bus accident that Tsukuyomi would have been caught in as well if not for Tsukasa Kadoya's intervention.

Personality
Tsukuyomi is a no-nonsense individual and shares relatively the same goals as Geiz, though she is prone to stopping Sougo from becoming Oma Zi-O by not having him transform, as opposed to Geiz's idea of outright killing him. Her conviction to her ideals is great enough that she would save Sougo from Geiz when the latter attempts to kill him. After hearing Sougo's conviction of wanting to become a good king, Tsukuyomi began to trust him as she found almost no evidence that Sougo would eventually become Oma Zi-O. However that conviction faltered slightly when Sougo acquired Zi-O II, which caused Tsukuyomi to become paranoid and begin to believe that Sougo could in fact become Oma Zi-O. She sides with White Woz in an attempt to stop him, though she eventually defended young Sougo in 2009 from Swartz and realized the future could indeed be changed.

When Tsukuyomi discovers her temporal abilities, she became shocked and horrified over this fact, but was later able to accept for who she was now, rather than who she was before.

She is also shown to appreciate different kinds of foods, such as Shouichi's cooking and sweets, although according to Geiz, she has a preference to really spicy items.

Powers and Equipment

 * Temporal Freezing: Through currently unknown means, Tsukuyomi shares the Time Jackers' ability to freeze time. Her ability is powerful enough to even freeze Swartz, something that both Heure and Ora cannot or do not have the authority to do. After learning to accept herself for what she was, she is able to control her ability at will, having used it to save innocent civilians from being crushed by following debris, and allowing allies to move within the confines of her time freezing. This ability may or may not be inherited. In the altered timeline, Tsukuyomi is fully aware of her powers and is able to use it to the best of its ability, though it can be easily canceled out by other Time Jackers.

Arsenal

 * Faizphone X
 * Time Mazine
 * Ziku Driver (gag only)
 * Tsukuyomi Ridewatch (gag only)

Relationships

 * Sougo Tokiwa/Kamen Rider Zi-O: Like Geiz, Tsukuyomi believes Sougo to be the evil tyrant Oma Zi-O and decided to go back in time to change his fate. At first, she seemed confused that a light-hearted teenager like Sougo could grow into an evil Demon King. But that quickly changes when she notices his earnest motivation to become a king and his ability to activate the Zi-O Ridewatch. Despite this, she wants to help and guide Sougo in being a hero as Zi-O so time and history can hopefully be altered for the better. But she then loses her faith in him when he becomes Zi-O II. She then reaffirms her mission to kill Sougo, even going as far as time traveling to 2009, seemingly to kill Sougo when he was still a child, while she actually protected the younger Sougo from Swartz after she learned the truth. Once discovering that Swartz was responsible for what had occurred and the possibility of Sougo's future as Oma Zi-O could be altered, her doubt was cast aside as both she and Geiz reconciled with him and return to 9 5 DO.
 * Geiz Myokoin/Kamen Rider Geiz: Geiz and Tsukuyomi were on the side determined to defeat Oma Zi-O in the year 2068. But after witnessing many casualties, Geiz came to the conclusion that he needs to kill the man who would become Oma Zi-O in the past. Tsukuyomi does not agree with this but Geiz goes back in time. She tries to protect Sougo from him, believing it's not right to kill him for something he hasn't even done yet. After Geiz tries to help Zi-O, she asks him to do what he come for. Although Tsukuyomi remains allies with Geiz, she decides to settle their mission on her own. Upon learning the whole truth, Tsukuyomi later convinces Geiz to postpone his and Sougo’s duel.
 * Black Woz: Tsukuyomi was once a Resistance member under Black Woz. However, after Black Woz betrayal, Tsukuyomi distrust her former captain, although she still remain civil to him. Black Woz on the other hand become worried after Tsukuyomi shows her ability to stop time temporarily and believes that Tsukuyomi might have been a Time Jacker before her amnesia.
 * White Woz: After Sougo became Zi-O II, Tsukuyomi chose to side with White Woz in order to change the future until she learned the truth of Sougo's past and being informed by Tsukasa Kadoya that the future could be changed.
 * Swartz: Swartz is in fact her older brother, though their relationship seems to have gone estranged since Tsukuyomi lost her memories and the way Swartz has been treating her since. However their interactions increased once Tsukuyomi's time-stopping abilities were re-awakened in her teen years.

Legend Riders

 * Tsukasa Kadoya/Kamen Rider Decade: Tsukuyomi was saved by Tsukasa during the bus accident in 2009. They both learn the whole truth about Sougo’s past and Tsukasa himself explained his motives to Tsukuyomi. Thanks to the knowledge, Tsukuyomi regained her faith in Sougo.
 * Shouichi Tsugami/Kamen Rider Agito: Tsukuyomi met Shouichi while she isolated herself from her fellow 9 5 DO members due to her newfound ability to freeze time and her unknown past due to her amnesia, something Shouichi could relate to. Thanks to Shouichi's wisdom, Tsukuyomi regains her self confidence and masters her ability.

Portrayal
Tsukuyomi is portrayed by Shieri Ohata (大幡 しえり).

Etymology
Her name comes from the moon god  of the Shinto religion and Japanese myth.