He is approached by the Libra Zodiarts, seeing him as a potential Horoscopes member, and is given a Zodiarts Switch that allows him to transform into the Perseus Zodiarts, arming him with the Oracle sword. He also has Medusa on his left arm, which enables him to turn anything he touches to stone. Motoyama uses his power to attack and petrify anyone and anything that interferes in his work's creation.
Even though his Last One form is destroyed by Kamen Rider Fourze Fire States, the Zodiarts Switch recreates the Perseus Zodiarts's body as he gains the ability to fire petrification beams from his Medusa hand. However, though Gentaro failed in his attempt to reach him by challenging him to a painting contest, the Perseus Zodiarts later realizes that he made a grave error in judgement over his actions by realizing that the perfection he sought is only in form and was for his own satisfaction only.
The Perseus Zodiarts then accepts Gentaro's friendship with the intent of returning to a human before the Libra Zodiarts converts him into a berserker for his Resurrection Star losing its glow. However, with the help of Kamen Rider Meteor holding the Libra Zodiarts at bay, Kamen Rider Fourze uses the Pen Switch to disable the berserk Perseus Zodiarts before destroying him. Back in his body, Motoyama is later seen creating a new painting to give to the kindergartners.