"Pieces" is an anime series that revolves around a group of high school students who become entangled in a series of mysterious and supernatural events. The narrative begins with the discovery of an ancient artifact, a puzzle box, hidden within the school grounds. This artifact, when activated, releases fragments of a forgotten past, each tied to a specific student. These fragments manifest as visions, memories, or physical phenomena, revealing secrets about the characters' lives and the school's history.

The protagonist, a reserved yet observant student named Haruto, inadvertently triggers the puzzle box during a school excavation project. As the fragments emerge, Haruto and his classmates—each with distinct personalities and backgrounds—begin to experience strange occurrences. These include unexplained disappearances, time loops, and encounters with shadowy figures. The fragments are revealed to be pieces of a larger narrative, one that connects the students to a tragic event that occurred decades earlier at the school.

Central to the story is the relationship between Haruto and his childhood friend, Aoi, who becomes increasingly affected by the fragments. Aoi's connection to the artifact grows stronger, leading to a gradual transformation that threatens her well-being. Other key characters include Riku, a skeptical but resourceful classmate who aids in uncovering the truth, and Yuna, a transfer student with her own mysterious ties to the artifact. Together, they work to piece together the fragmented history and confront the malevolent force behind the disturbances.

The plot unfolds through a series of interconnected episodes, each focusing on a specific fragment and its impact on the characters. As the students delve deeper, they uncover the story of a former student who sought to harness the artifact's power, leading to a catastrophic event that left the school cursed. The narrative builds toward a climactic confrontation, where the students must decide whether to destroy the artifact or use its power to rewrite the past, risking unforeseen consequences.

Themes of memory, identity, and the consequences of tampering with the unknown are explored throughout the series. The fragmented structure of the story mirrors the puzzle box itself, with each revelation adding depth to the overarching mystery. The characters' personal struggles and growth are interwoven with the supernatural elements, creating a balance between emotional drama and suspense. The series concludes with a resolution that ties together the fragmented narrative, leaving some questions unanswered to emphasize the lingering impact of the events on the characters' lives.