"Sekiei Ayakashi Mangatan" is a supernatural anime series set in a world where humans coexist with ayakashi, mystical beings that embody various forms of folklore and myth. The narrative centers on a young man named Haruto, who inherits an ancient bookstore from his late grandfather. This bookstore, however, is no ordinary shop—it serves as a gateway between the human world and the realm of ayakashi. Haruto discovers that he has also inherited the role of a mediator, tasked with maintaining the balance between these two worlds and resolving conflicts that arise between humans and ayakashi.

The story unfolds as Haruto encounters a diverse array of ayakashi, each with their own unique abilities, personalities, and motivations. Some ayakashi seek to coexist peacefully with humans, while others harbor malicious intentions, leading to tension and conflict. Haruto is aided by a small group of allies, including a tsukumogami (a spirit inhabiting an object) named Koto, who takes the form of a talking book, and a mysterious ayakashi named Yuki, who becomes his protector and guide. Together, they navigate the complexities of the ayakashi world, uncovering secrets about Haruto's family lineage and the true purpose of the bookstore.

As the series progresses, Haruto faces increasingly dangerous challenges, including powerful ayakashi who threaten to disrupt the balance between worlds. The narrative explores themes of coexistence, responsibility, and the blurred lines between good and evil. Haruto's growth as a mediator is central to the plot, as he learns to harness his own latent abilities and confronts the moral dilemmas that arise from his role. The series balances episodic storytelling with an overarching plot, gradually revealing the deeper mysteries of the ayakashi realm and Haruto's connection to it. The interplay between human and supernatural elements drives the narrative, creating a rich and immersive world filled with intrigue and danger.