"No. 5" is a science fiction manga series set in a dystopian future where humanity has been ravaged by environmental collapse and war. The story revolves around the Rainbow Council, a group of genetically engineered super-soldiers known as the "Numbers," who were created to maintain order in a fractured world. Each member of the Council possesses unique abilities and is assigned a specific role. The protagonist, No. 5, is one of these soldiers, distinguished by his exceptional combat skills and a deep sense of empathy that sets him apart from his peers.

The narrative begins with No. 5 abandoning his post and fleeing the Rainbow Council after forming a bond with a mysterious woman named Matryoshka, who harbors a secret tied to the Council's origins. This act of desertion triggers a manhunt led by the other Numbers, who are determined to eliminate No. 5 for betraying their mission. As No. 5 and Matryoshka journey across a desolate and war-torn landscape, they uncover the dark truths behind the Rainbow Council's creation and the oppressive system it upholds. The story explores themes of identity, free will, and the consequences of humanity's reliance on technology and genetic manipulation.

The supporting cast includes other members of the Rainbow Council, each with distinct personalities and abilities. No. 1, the stoic and ruthless leader, serves as the primary antagonist, embodying the Council's rigid ideology. No. 3, a pragmatic and calculating operative, contrasts with No. 5's idealism, while No. 9, a childlike yet deadly assassin, adds complexity to the group dynamics. The interactions between these characters highlight the moral ambiguities of their roles and the ethical dilemmas they face.

The plot is driven by a series of intense confrontations and philosophical debates, as No. 5 grapples with his purpose and the nature of his existence. The manga's pacing alternates between action-packed sequences and introspective moments, creating a balance between external conflict and internal exploration. The world-building is intricate, with detailed depictions of a society on the brink of collapse, where advanced technology coexists with primal survival instincts.

Throughout the series, the relationship between No. 5 and Matryoshka serves as a central emotional anchor, challenging the protagonist's understanding of loyalty and humanity. Their journey is marked by sacrifice, betrayal, and the pursuit of a fragile hope for a better future. The narrative concludes with a resolution that underscores the cyclical nature of conflict and the enduring struggle for freedom and self-determination.