"Kurenai" centers on Shinkurou Kurenai, a 16-year-old dispute mediator living in a rundown apartment complex. His job involves resolving conflicts between individuals, often through unconventional and morally ambiguous methods. Shinkurou works under the guidance of Benika Juuzawa, a powerful and enigmatic woman who runs the mediation service. His life takes a dramatic turn when he is tasked with protecting Murasaki Kuhouin, a sheltered and naive seven-year-old girl from a wealthy and influential family. Murasaki has been raised in isolation, unaware of the outside world, and her sudden arrival in Shinkurou's life forces him to navigate unfamiliar responsibilities.

The narrative explores the evolving relationship between Shinkurou and Murasaki as they adjust to their new circumstances. Shinkurou, initially reluctant and ill-prepared for the role of a guardian, gradually develops a sense of duty and affection for Murasaki. Her innocence and curiosity challenge his cynical worldview, while her presence exposes him to the complexities of her family's dark secrets. The Kuhouin family, a powerful and secretive clan, becomes a central source of conflict as they seek to reclaim Murasaki, revealing their involvement in political intrigue and morally questionable practices.

As the story progresses, Shinkurou and Murasaki form a bond that transcends their initial roles, with Shinkurou determined to protect her from the dangers posed by her family and their enemies. The series delves into themes of family, loyalty, and the clash between innocence and corruption, set against a backdrop of urban decay and societal tension. Supporting characters, such as Shinkurou's neighbors and colleagues, add depth to the narrative, providing both comedic relief and insight into the protagonist's struggles.

The plot balances moments of lighthearted interaction between Shinkurou and Murasaki with intense action sequences and emotional confrontations. The series maintains a focus on character development, particularly Shinkurou's growth from a detached mediator to a committed protector. Murasaki's journey from a sheltered child to someone who begins to understand the complexities of the world around her is equally central to the story. "Kurenai" weaves together elements of drama, action, and introspection, creating a narrative that is both engaging and thought-provoking.