"A Lollipop or a Bullet" is a psychological thriller manga that explores themes of identity, morality, and the consequences of power. The narrative centers on a high school student named Yuki, who leads a double life. By day, Yuki is an unassuming, quiet student, but by night, they become a vigilante known as "Lollipop," targeting corrupt individuals and delivering justice through violent means. The alias "Lollipop" stems from the character's signature calling card: leaving a lollipop at the scene of their crimes, symbolizing a twisted sense of reward or punishment.

The story begins with Yuki's transformation into this vigilante persona, driven by a traumatic past involving the death of a loved one due to systemic corruption. As Lollipop's actions gain notoriety, law enforcement, led by Detective Kurosawa, begins to close in. Kurosawa is a seasoned investigator with a personal vendetta against vigilantes, having lost a colleague to a similar figure in the past. The cat-and-mouse dynamic between Yuki and Kurosawa forms the backbone of the plot, with each character's motivations and moral ambiguities gradually revealed.

Yuki's dual life becomes increasingly complicated as their actions attract the attention of both allies and enemies. Among these is Aya, a classmate who becomes suspicious of Yuki's behavior and begins to uncover their secret. Aya's involvement adds a layer of tension, as her curiosity threatens to expose Yuki while also forcing them to confront the human cost of their actions. Meanwhile, a shadowy organization known as "The Syndicate" emerges, revealing that Yuki's vigilantism has disrupted a larger network of corruption, putting them in direct conflict with powerful figures who will stop at nothing to eliminate the threat.

The manga delves into the psychological toll of Yuki's choices, portraying their internal struggle between the desire for justice and the fear of losing their humanity. Flashbacks and fragmented memories provide insight into Yuki's past, revealing the events that shaped their worldview and fueled their crusade. The narrative also examines the broader societal implications of vigilantism, questioning whether individuals can truly enact change outside the system or if they inevitably become part of the cycle of violence they seek to dismantle.

As the story progresses, the lines between right and wrong blur, with characters facing moral dilemmas that challenge their beliefs. The climax revolves around a high-stakes confrontation between Yuki, Kurosawa, and The Syndicate, culminating in a resolution that leaves lasting consequences for all involved. The manga concludes with an open-ended exploration of justice, redemption, and the cost of wielding power, leaving readers to reflect on the complexities of its themes.