"The Night Beyond the Tricornered Window" is a supernatural mystery anime based on the manga by Tomoko Yamashita. The narrative centers on Mikado Kousuke, a reserved bookstore employee with the ability to see spirits, and Hiyakawa Rihito, a mysterious exorcist who manipulates spiritual energy. The two form an unlikely partnership after Hiyakawa discovers Mikado’s spiritual sensitivity and recruits him to assist in exorcising malevolent entities. Their collaboration deepens as they investigate a series of supernatural incidents tied to a dark, enigmatic force.

The story unfolds as Mikado and Hiyakawa delve into cases involving cursed objects, haunted locations, and vengeful spirits. Their investigations reveal a connection to a powerful entity known as the "Eye," which Hiyakawa seeks to control for his own purposes. Mikado, initially reluctant and wary of Hiyakawa’s methods, becomes increasingly entangled in the exorcist’s dangerous pursuits. The dynamic between the two characters is marked by tension and dependency, as Mikado’s spiritual abilities grow stronger and Hiyakawa’s motives remain ambiguous.

Supporting characters include Erika Hiura, a journalist and Mikado’s childhood friend, who becomes involved in their supernatural cases, and Detective Sakaki, a police officer who occasionally assists them. The series explores themes of trust, power, and the consequences of meddling with the supernatural. As the plot progresses, Mikado and Hiyakawa confront their own vulnerabilities and the moral complexities of their actions, culminating in a confrontation with the "Eye" and its far-reaching influence.

The anime blends psychological tension with supernatural horror, maintaining a focus on the evolving relationship between Mikado and Hiyakawa. The narrative balances episodic cases with an overarching plot, creating a cohesive exploration of its characters and the eerie world they inhabit. The series concludes with unresolved questions, leaving room for further exploration of its themes and character dynamics.