"The Night Beyond the Tricorner Window" is a supernatural mystery manga that blends elements of horror, psychological tension, and the occult. The narrative centers on Mikado Kousuke, a socially anxious bookstore employee who possesses the ability to see ghosts and spirits. His life takes a dramatic turn when he encounters Hiyakawa Rihito, a mysterious and enigmatic exorcist who can not only see spirits but also consume them. The two form an unlikely partnership, with Mikado reluctantly assisting Hiyakawa in his exorcism work, despite his discomfort with Hiyakawa's unsettling methods and personality.

As the story progresses, the duo becomes entangled in increasingly dangerous supernatural cases, often involving malevolent spirits and dark rituals. Mikado's ability to see spirits and Hiyakawa's power to devour them create a dynamic that is both symbiotic and fraught with tension. Their investigations lead them to uncover a deeper, more sinister connection between the spiritual world and their own lives, particularly involving a series of murders linked to occult practices. The narrative delves into themes of trauma, guilt, and the blurred lines between the living and the dead, as Mikado and Hiyakawa confront their own pasts and the consequences of their abilities.

The characters are complex and layered, with Mikado serving as the emotional anchor of the story. His vulnerability and moral dilemmas contrast sharply with Hiyakawa's detached and often morally ambiguous demeanor. Hiyakawa's motivations remain shrouded in mystery for much of the series, adding an element of unpredictability to their partnership. Supporting characters, such as Erika Hiura, a police officer who becomes involved in their cases, and other individuals connected to the occult, further enrich the narrative by providing additional perspectives and stakes.

The plot is driven by a series of interconnected cases, each revealing more about the overarching mystery surrounding the tricorner window—a supernatural phenomenon that serves as a gateway between worlds. The tension escalates as Mikado and Hiyakawa uncover the truth behind the window and its connection to a powerful and malevolent entity. The manga balances episodic storytelling with a larger, overarching narrative, creating a sense of progression and deepening intrigue as the stakes grow higher.

"The Night Beyond the Tricorner Window" is a compelling exploration of the supernatural, characterized by its intricate plotting, psychological depth, and the evolving relationship between its two central characters. The series maintains a consistent tone of unease and suspense, making it a standout in the genre of supernatural horror and mystery.