"A Piece of Phantasmagoria" is a supernatural mystery series set in a world where reality and illusion intertwine. The narrative centers on Kaito Tachibana, a high school student who discovers an ancient, sentient artifact known as the Phantasmagoria Fragment. This artifact grants its wielder the ability to manipulate dreams and memories, but at the cost of blurring the line between the real and the imagined. Kaito’s life takes a dramatic turn when he encounters a mysterious girl named Aya Kagami, who claims to be a "Dreamweaver" tasked with protecting the balance between the waking world and the dream realm.

The story unfolds as Kaito and Aya investigate a series of bizarre incidents linked to the misuse of the Fragment’s power. These incidents involve individuals whose repressed memories and desires manifest as distorted dreamscapes, threatening to consume their sanity and spill over into reality. As they delve deeper, they uncover a hidden organization, the Nocturne Syndicate, which seeks to exploit the Fragment’s power to reshape the world according to their own twisted ideals. The Syndicate’s leader, a enigmatic figure known only as "The Conductor," possesses a Fragment of his own, setting the stage for a clash of ideologies and powers.

Kaito’s journey is marked by his struggle to understand the Fragment’s true nature and his own role in the unfolding events. Aya, meanwhile, grapples with her duty as a Dreamweaver and her growing attachment to Kaito, which complicates her mission. Supporting characters include Rina Fujisaki, a classmate with a keen interest in the supernatural, and Haruto Soma, a former Dreamweaver who harbors a personal vendetta against the Nocturne Syndicate. Each character’s backstory and motivations are gradually revealed, adding layers to the overarching narrative.

The plot is driven by a series of episodic encounters with individuals affected by the Fragment’s power, interspersed with larger arcs that advance the central conflict. Themes of identity, memory, and the nature of reality are explored as Kaito and his allies confront the consequences of tampering with the dream world. The series builds toward a climactic confrontation with the Nocturne Syndicate, culminating in a resolution that challenges the characters’ understanding of their own existence and the boundaries between dreams and reality.