Oma's Day

Oma's Day (オーマの日) is an anticipated event serving as one of the central plot points in Kamen Rider Zi-O. According to Tsukuyomi and Geiz Myoukouin, it is said to be set sometime in the year 2019. Due to the present day Zi-O temporarily giving up his Ziku-Driver, the expected progression of events in Oma's Day now differ across separate timelines.

Oma Zi-O's timeline
On this day, Zi-O will transform into Oma Zi-O and control seven giant monstrous machines called Dai Mazines to destroy the world along with all Kamen Riders and become the "Demon King." This global catastrophe will create the dystopian timeline where Geiz Myoukouin, Tsukuyomi and the original Woz came from.

Geiz Revive's timeline
On this day, Geiz Revive will defeat Oma Zi-O and save the world, becoming its savior and creating a new history. Sometime after this day, Another Woz will travel to January 2019 to assist Geiz. This is also the timeline where future Kamen Riders Shinobi, Quiz and Kikai hail from.