"SP Baby" is a manga series that blends romance, action, and drama, centering on the life of Tamaki Hasegawa, a young woman who becomes an unlikely bodyguard. Tamaki, a former delinquent with a strong sense of justice and impressive combat skills, is thrust into the world of high-stakes security when she saves the life of a young boy, Sena Izumi, from a kidnapping attempt. Sena is the son of a prominent politician, and his family hires Tamaki as his personal bodyguard, or "SP" (Security Police), due to her quick thinking and physical prowess.

The narrative explores Tamaki's adjustment to her new role, balancing her tough exterior with the responsibilities of protecting Sena. Despite her initial reluctance, she forms a close bond with the boy, who is mature beyond his years and often acts as a grounding force for Tamaki. Their relationship evolves from professional to familial, with Tamaki becoming a protective older sister figure. The story delves into the challenges they face together, including political intrigue, assassination attempts, and the emotional toll of living under constant threat.

Key characters include Sena Izumi, the precocious and kind-hearted child who relies on Tamaki for safety and companionship, and Kagetora Sugou, a seasoned bodyguard who becomes Tamaki's mentor. Kagetora provides guidance and support, helping Tamaki navigate the complexities of her role while also challenging her to grow. The series also introduces antagonists tied to the political landscape, whose motives and actions drive much of the conflict.

The plot is structured around episodic missions and overarching threats, with Tamaki and Sena facing various dangers while uncovering deeper conspiracies. Themes of loyalty, family, and personal growth are central, as Tamaki learns to reconcile her past with her present responsibilities. The series balances intense action sequences with moments of emotional depth, creating a dynamic and engaging narrative.