Chief Ace Shimizu is a demonic entity originating from the parallel dimension Makai, embodying a fictional persona mirroring real-life Seikima-II band member Ace Shimizu. Within the narrative of "Seikima II Humane Society - Jinruiai ni Michita Shakai", he serves as Chief among a quintet of demons led by Demon Kogure (later Demon Kakka). His background involves spearheading a plot to annihilate humanity by activating the ultimate weapon, the Tower of Babel. This plan is opposed by Rosa, the reformed war goddess Freyja, who constructs the countermeasure Tower of Cain. During the climax, the demons successfully activate the Tower of Babel. However, Demon Kogure dramatically shifts their objective, abandoning world destruction to form a rock band and spread demonic influence through music. Consequently, Chief Ace Shimizu transitions from his destructive role into the newly formed band Seikima-II, adopting the stage identity of his real-world counterpart. This character arc concludes within the OVA.