Oma's Day

Villainous Event
Full Name	Oma's Day
Alias	Ohma's Day
Origin	Kamen Rider Zi-O
Location	Japan
Orchestrators	Swartz Quartzer
Known Factions	Dai Mazines
Purposes	Ascend Sougo Tokiwa as Oma Zi-O. Unify all the Rider timelines into one so the Quartzers can enact their plan.
Type of Villainous Event	Oppression

Oma's Day is the day on which Sougo Tokiwa ascended as Oma Zi-O in Kamen Rider Zi-O.

On April 17, 2019, Sougo Tokiwa collected the powers of all 20 Heisei Kamen Riders and used them to become Oma Zi-O. With his new power, Sougo ravaged the world using the Dai Mazines and killed off half the human population before declaring himself king of the world.

History

Sougo's ascension as Oma Zi-O was masterminded by the Time Jacker Swartz as well as the Quartzer. The Quartzer sought to use Sougo to unify the Rider timelines into a single world by having him collect the Ridewatches. After the Quartzer leader imbued Sougo with power, Swartz selected him from within a group of children to become his chosen Demon King.

Spurred on by Swartz's words, which he believed to have come to him in a dream, Sougo began his hunt to collect the Ridewatches from all 20 of the main Heisei Kamen Riders so he could become king. Once he had gathered them all, Sougo used them to become Oma Zi-O. He then sent Dai Mazines to the corners of the world to reduce it to a wasteland, killing half the human population in the process.

However, the timeline became altered when two members of the resistance against Oma Zi-O, Tsukuyomi and Geiz, traveled back in time to stop his rise. In response, the Quartzers and Oma Zi-O sent their operative Woz back in time to ensure he stayed on track to become Oma Zi-O. Also traveling back in time were Swartz and two other Time Jackers he had recruited, Heure and Ora. Swartz had convinced them that they would be finding an Another Rider to supplant Oma Zi-O as the future Demon King and allow them to rule through it, when in fact their true purpose was to create foes to incentivize Sougo to gather the Ridewatches.

The alterations to the timeline would result in a new possible future emerging, in which Geiz assumed a new form called Geiz Revive on Oma's Day and defeated Sougo before he could destroy the world. Ultimately, neither of the futures came to pass as Sougo and Geiz instead reconciled.

Oma's Day would still occur however on a later date, when Swartz forcibly merged a bunch of timelines together as part of his endgame plan to force Sougo to become Oma Zi-O. After Swartz killed both Tsukuyomi and Geiz, an enraged Sougo finally ascended as Oma Zi-O and used his power to kill Swartz, before resetting everything to normal in order to bring back Tsukuyomi and Geiz and undo all the damage that had been caused.