Orochi, also known as Yamata no Orochi, is the ancient evil deity and primary antagonist across all media. It seeks to replace the world with darkness and nihilism. Its influence manifests through eight human disciples, termed "necks" or "heads," each granted fragmented power and a unique mecha. These disciples are individuals who suffered profound pain or despair, including a sociopathic criminal, an unintelligent brute, a disillusioned nun, a former pop idol, an antisocial manga artist, a catgirl, and a seemingly traitorous friend. Only one disciple, Sōma Ōgami, can temporarily resist Orochi's control.

The disciples exhibit exaggerated personalities and distinct powers like teleportation, levitation, or specialized weapons. They operate uncooperatively initially, rarely coordinating attacks against the Solar and Lunar Priestesses, Himeko and Chikane, until midway through the series. Orochi punishes any disciple resisting its influence, though Tsubasa—the first head and a former criminal—eventually defies it to protect his brother Sōma. Each disciple pilots a distinct mecha representing a fragment of Orochi's power, such as Take no Yasukunazuchi (winged swords) and Yatsu no Onokoshizuchi (tentacled demon). During the final confrontation, Orochi amalgamates these mechas into a singular, colossal entity to battle Ame no Murakumo.

Orochi resides within a personal dimension resembling a dark realm, featuring individualized spaces for each disciple. Its history remains consistent: Orochi cyclically reawakens to engulf the world, opposing Ame no Murakumo and the reincarnated priestesses. After defeat, Orochi's purified disciples are restored to life with no memory of their service. Within the series' Japanese mythological context, Orochi is loosely adapted from the eight-headed serpent historically defeated by Susanoo.

No significant deviations in Orochi's role or background occur in spin-offs like *Himekami no Miko*. The character functions as a persistent force of destruction, countered through cyclical battles.