"Sanninme ga Kieta" is a psychological mystery manga that revolves around the disappearance of a third person in a series of interconnected events. The narrative begins with a seemingly ordinary high school setting, where three students—Yui, Haruto, and Akira—form a close-knit friendship. Their lives take a dark turn when Yui suddenly vanishes without a trace, leaving behind only cryptic clues. Haruto and Akira, determined to uncover the truth, embark on an investigation that leads them into a labyrinth of secrets, lies, and psychological manipulation.

As the story progresses, it becomes evident that Yui’s disappearance is not an isolated incident. It is linked to a pattern of similar vanishings, each involving a trio of individuals where the third person mysteriously disappears. The manga delves into the psychological toll on Haruto and Akira as they grapple with guilt, paranoia, and the fear that one of them might be next. Their investigation uncovers a shadowy organization orchestrating these events, using psychological experiments to test the limits of human relationships and loyalty.

The characters are intricately developed, with Haruto portrayed as the rational and determined investigator, while Akira struggles with emotional instability and a growing sense of distrust. Yui, though absent for much of the story, is revealed through flashbacks and memories, highlighting her pivotal role in the trio’s dynamic. The narrative explores themes of trust, identity, and the fragility of human connections, as the characters are forced to confront their own vulnerabilities and the possibility that they may have been complicit in the events unfolding around them.

The plot is structured around a series of twists and revelations, each deepening the mystery and raising the stakes for the protagonists. The manga’s pacing alternates between moments of intense suspense and quieter, introspective scenes that delve into the characters’ psyches. The climax reveals the true nature of the organization’s experiments and the fate of the missing individuals, culminating in a resolution that leaves lingering questions about the nature of free will and the consequences of human actions. "Sanninme ga Kieta" is a gripping exploration of psychological tension and the complexities of human relationships, set against the backdrop of a meticulously crafted mystery.