"Zenki" is a supernatural action anime series centered around the ancient demon Zenki, who is sealed within a young girl named Chiaki Enno. Chiaki is the descendant of a powerful priestess who originally sealed Zenki 1,200 years ago to prevent him from wreaking havoc. The story begins when a malevolent force, led by the demon Karuma, seeks to resurrect the evil god Anki, Zenki's counterpart. To combat this threat, Chiaki must awaken and control Zenki, transforming him from a destructive force into a protector of humanity.

Zenki, once awakened, is a formidable warrior with immense strength and magical abilities. However, his power is tied to Chiaki's spiritual energy, and he can only maintain his full strength for a limited time. The dynamic between Chiaki and Zenki is central to the narrative, as Chiaki struggles to harness her latent powers while Zenki grapples with his dual nature as both a demon and a protector. Together, they form an uneasy alliance to thwart Karuma's plans and prevent the resurrection of Anki.

The series features a mix of episodic battles and overarching plotlines, with Chiaki and Zenki facing various demons and supernatural challenges. Supporting characters include Goki, a loyal and comedic sidekick who aids Chiaki, and other allies who join their cause. The antagonists, led by Karuma, are driven by their desire to unleash Anki and plunge the world into chaos. As the story progresses, the stakes escalate, culminating in a climactic confrontation between Zenki and Anki.

Themes of redemption, the balance between good and evil, and the power of human determination are woven throughout the narrative. The series blends action, humor, and supernatural elements, creating a fast-paced and engaging storyline. "Zenki" explores the complexities of its characters, particularly Zenki's internal conflict and Chiaki's growth as a priestess, while delivering a compelling tale of heroism and sacrifice.