"Spiral" is a mystery-thriller manga series centered around Ayumu Narumi, a high school student whose life becomes entangled in a complex web of conspiracies and enigmatic events following the sudden disappearance of his older brother, Kiyotaka Narumi. Kiyotaka, a renowned detective, vanishes without a trace, leaving behind only cryptic clues and a lingering sense of unease. Ayumu, though initially reluctant to follow in his brother's footsteps, is drawn into the investigation when he encounters a series of bizarre incidents tied to a shadowy organization known as the "Blade Children."

The Blade Children are a group of individuals with mysterious origins, each marked by a unique spiral-shaped birthmark and possessing extraordinary abilities. They are pursued by a secretive group called the "Hunters," who seek to eliminate them. Ayumu's involvement deepens when he meets Hiyono Yuizaki, a curious and resourceful classmate who becomes his ally in unraveling the mysteries surrounding the Blade Children and his brother's disappearance. Together, they navigate a labyrinth of puzzles, codes, and dangerous confrontations, uncovering the truth piece by piece.

As the story progresses, Ayumu discovers that Kiyotaka's disappearance is linked to the Blade Children and their connection to a larger conspiracy involving genetic experimentation and a prophecy foretelling their role in shaping the future. The narrative explores themes of identity, fate, and the moral ambiguity of those who seek to control or destroy the Blade Children. Key characters include Eyes Rutherford, a Blade Child with a calm demeanor and a tragic past, and Kousuke Asazuki, a Hunter with conflicting motivations. The series balances intricate plot developments with moments of tension and emotional depth, culminating in a resolution that ties together the fates of the Blade Children, Ayumu, and the legacy of his brother.