"Five Numbers!" is a four-episode original net animation (ONA) set in a futuristic prison facility known as Boxman Hachigou, a high-security space station designed to hold the most dangerous criminals. The story centers around a group of five inmates who are abruptly awakened from cryogenic sleep by a mysterious system failure. The group includes Joe, a former soldier; Nico, a skilled hacker; Gouri, a strong but simple-minded man; Touko, a sharp and resourceful woman; and Tanaka, a quiet and enigmatic figure. Each character possesses unique skills and a troubled past, which gradually come to light as the narrative unfolds.

The inmates discover that the prison's automated systems have malfunctioned, leaving them stranded and under threat from the station's security measures. As they attempt to navigate the labyrinthine facility, they uncover clues suggesting that their awakening was not accidental. Tensions rise as the group struggles to trust one another, with hidden agendas and personal motivations complicating their efforts to survive. The story delves into themes of betrayal, redemption, and the consequences of past actions, as the characters confront both external dangers and their own inner demons.

The plot intensifies as the group learns about the existence of a sixth prisoner, whose presence is shrouded in mystery and who may hold the key to their escape—or their doom. The narrative builds toward a climactic confrontation, revealing the true nature of the prison and the reasons behind their imprisonment. The series combines elements of science fiction, psychological drama, and action, creating a tightly paced story that explores the complexities of human nature under extreme circumstances. The characters' interactions and evolving dynamics drive the narrative, culminating in a resolution that leaves lingering questions about justice, freedom, and the cost of survival.