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The mysterious leader of the Quartzer, who has the power to transform into Kamen Rider Barlckxs, is the primary antagonist of the movie Kamen Rider Zi-O: Over Quartzer, as well as the overarching antagonist of Kamen Rider Zi-O as a whole.
A powerful figure who is revealed to be the superior of Woz, he is the original version of Sougo Tokiwa, also referred to as SOUGO, who reigns as King of Time in an alternate reality and is the one behind his alternate past self's rise into Oma Zi-O. His ultimate goal is to erase the history of the Kamen Riders in order to create a new world.
He is portrayed by Japanese singer ISSA, who also performs Kamen Rider Zi-O's opening theme, Over "Quartzer".
After Sougo was abducted along with several other children by Swartz, his alternate self bestowed time powers onto him so he would be selected as king, beginning Sougo's journey into Oma Zi-O.
In order to ensure past Sougo Tokiwa would become Oma Zi-O in the future, the leader of the Quartzer supplied Woz with the Oma Advent Calendar and sent him back in time with the knowledge of future events to guide his past self into becoming the Demon King.
After Sougo unlocked the power of GrandZi-O, the Quartzer leader sent Kagen and Jogen to the Sengoku Era to eliminate Krim Steinbelt's ancestor and thus prevent the creation of the Drive Driver, which would in turn negate the GrandZi-O Ridewatch.
After Sougo receives the Drive Ridewatch from Krim Steinbelt and finishes collecting all the Ridewatches, Woz stole all the Ridewatches to deliver them to SOUGO, who appears to his alternate self seated on the throne with the other Quartzers standing on either side of him. Introducing the Quartzer as the "Wardens of History", SOUGO transforms into Kamen Rider Barlckxs and swiftly defeats Zi-O before having him imprisoned. With his alternate self out of the way, SOUGO commences his ultimate plan: to use a portal to smash the World of Zi-O into his own world and erase the history of the Kamen Riders, thus creating a new world for him to rule over as king of time.
However, Oma Zi-O then interferes to prevent SOUGO from altering the future and gives present Sougo the Oma Zi-O Ridewatch, which Sougo uses to transform into Kamen Rider Zi-O Oma Form and summon the past 19 Heisei Kamen Riders to do battle with SOUGO and his army of Dai Mazines and Kasshins. Seeing this, Woz defects from the Quartzer and returns to Sougo's side, tearing pages out from the Oma Advent Calendar and causing the portal to stop functioning. As the Riders destroy the Dai Mazines, Barlckxs stabs Woz with his Quarcane as punishment for his betrayal before facing the Heisei Riders. Barlckxs uses Black RX's BioRider and J's Ridewatch to grow giant and fights off all of the Riders with his tremendous power. However, refusing to give up, Zi-O and the other Kamen Riders all perform their Rider Kicks on Barlckxs and use their combined power to destroy the Quartzer Leader.
- Kamen Rider Barlckxs' name and design are based off of Kamen Rider Black RX, which premiered in the Showa Era but is considered a "lost Heisei Rider" in the movie due to also airing in the Heisei era.