Dekao begins as a human fighter battling Mikami Inaba on a school rooftop. Their struggle breaks nearby rabbit cages, causing both to fall; Mikami fuses with a rabbit during the descent. Following his defeat and fall, Dekao is captured by the mysterious organization SP or PS. They reconstruct him into a cyborg with enhanced physical capabilities, rocket propulsion, and increased strength. This organization seeks the power of human-animal merging and employs Dekao as an elite operative, an "admonisher," tasked with eliminating merged beings when standard operatives fail.

His cybernetic augmentation grants him an electronic eye providing targeting capabilities, rocket fists, and shoulder-mounted missiles. He engages Mikami Inaba (and her merged form, Mimika) in subsequent battles, including one on a public beach, but suffers defeat each time. After each failure, the organization further modifies his body. In his third appearance, he is reduced to a head and torso mounted on a mechanical horse-like body resembling an armored centaur. In his final known form, only his head remains, integrated into a large war machine on tank treads; deployed via helicopter, this form is dropped through a shopping mall skylight to confront Mikami and another merged being, Nekoi Koshka. Despite extensive cybernetic upgrades across four major confrontations, Dekao is consistently defeated, maintaining a record of zero successes.

His electronic eye depicts his targeting perspective during combat. The organization's repeated reconstructions of Dekao demonstrate their determination to eradicate merged beings, though his defeats contribute to their operational failures.