"Rose Guns Days Season One" is set in a fictional, post-World War II Japan, where the country has been divided and occupied by four foreign powers: the United States, Britain, the Soviet Union, and China. The story unfolds in a dystopian version of Tokyo, now renamed "Primrose," which has become a lawless city rife with corruption, crime, and political intrigue. The narrative centers on the struggle for power and survival among various factions, including the yakuza, foreign occupiers, and resistance groups.

The protagonist, Leo Shishigami, is a former soldier who becomes embroiled in the city's underworld after returning to Primrose. Leo is a skilled fighter with a strong sense of justice, but his ideals are tested as he navigates the morally ambiguous landscape of the city. He forms an alliance with Rose Haibara, a mysterious and resourceful woman who runs a nightclub called "Club Primavera." Rose is a key figure in the resistance movement against the foreign occupiers, and her club serves as a front for covert operations. Together, Leo and Rose work to undermine the oppressive forces controlling Primrose.

Another central character is Keith Woodman, a British intelligence officer who initially appears as an antagonist but later becomes a complex figure with his own motivations and loyalties. Keith's interactions with Leo and Rose reveal the intricate web of alliances and betrayals that define the city's power dynamics. The story also explores the lives of other characters, such as Stella Unwin, a young woman with a tragic past who becomes involved in the resistance, and Clarence, a ruthless yakuza leader with his own agenda.

The plot is driven by a series of escalating conflicts, including political assassinations, espionage, and large-scale battles between rival factions. Themes of loyalty, betrayal, and the cost of power are explored as the characters grapple with their personal and political struggles. The narrative is marked by its intricate plotting, with multiple storylines converging in unexpected ways, and its exploration of the moral complexities of war and occupation.

"Rose Guns Days Season One" combines elements of action, drama, and political intrigue, creating a compelling and multifaceted story. The series is notable for its well-developed characters, intricate world-building, and the tension-filled atmosphere of a city on the brink of chaos. The interplay between the personal and political dimensions of the story adds depth to the narrative, making it a standout work in the genre.