"Kyōsō no Simulacra" is a psychological thriller manga that explores themes of identity, memory, and the nature of reality. The narrative centers on a young man named Kōhei, who awakens in a mysterious facility with no recollection of his past. He discovers that he is part of an experiment involving "Simulacra," artificial beings designed to replicate human emotions and memories. These Simulacra are indistinguishable from real humans, and their purpose is to replace individuals in society, raising questions about what it means to be human.

Kōhei is assigned to interact with a Simulacrum named Aya, who is modeled after a deceased girl. As Kōhei spends time with Aya, he begins to recover fragments of his memories, which are intertwined with the life of the original Aya. The facility's enigmatic director, Dr. Sōma, oversees the experiment and manipulates the participants, often blurring the lines between truth and deception. Dr. Sōma's motives remain ambiguous, adding to the tension and uncertainty that permeates the story.

The plot thickens as Kōhei uncovers disturbing truths about the facility and its experiments. He learns that the Simulacra are not merely replicas but are capable of developing genuine emotions and self-awareness. This revelation forces Kōhei to confront ethical dilemmas about the treatment of these artificial beings and the morality of the experiment itself. His growing bond with Aya complicates matters, as he struggles to reconcile her existence with the memories of the original Aya.

Supporting characters include other participants in the experiment, each grappling with their own fragmented memories and identities. These individuals contribute to the overarching mystery, as their interactions with the Simulacra reveal deeper layers of the facility's agenda. The narrative is driven by a series of twists and revelations, keeping the reader engaged as the true nature of the experiment and the characters' roles within it are gradually unveiled.

The story is marked by its exploration of existential themes, such as the fluidity of identity and the ethical implications of creating sentient beings. The tension between reality and illusion is a recurring motif, as characters question the authenticity of their memories and relationships. The manga's pacing is deliberate, allowing for a gradual buildup of suspense and emotional depth as the characters' struggles and the facility's secrets come to light.