The character that appeared in Masked Rider Zi-O OverQuartzer was Shotaro Ishimori. He was one of the main villains in Masked Rider Zi-O and was also one of his plans and goals. Shotaro Ishimori was a mad scientist who tried to control the flow of time to control the entire world. He created the OverQuartzer to fight Zi-O and tried to achieve his plan by controlling Zi-O's timer. Eventually, the battle between Zi-O and OverQuartzer plunged the world into chaos and panic.