"Toku Touken Ranbu: Hanamaru ~Setsugetsuka~" is a continuation of the "Touken Ranbu: Hanamaru" series, which is based on the popular "Touken Ranbu" browser game. The story revolves around anthropomorphized historical swords, known as Touken Danshi, who are tasked with protecting history from the Time Retrograde Army, a group seeking to alter the past. The series is set in the Honmaru citadel, where these sword warriors reside and prepare for missions to safeguard historical events.

The narrative in "Setsugetsuka" focuses on the seasonal changes and the emotional growth of the Touken Danshi as they face new challenges. The story is episodic, with each episode often highlighting a specific character or group of characters, delving into their backstories and relationships. The overarching plot involves the Touken Danshi embarking on missions to various historical periods, where they confront the Time Retrograde Army and ensure that history remains unchanged. These missions are interspersed with moments of daily life at the citadel, showcasing the camaraderie and personal struggles of the characters.

Key characters include Yamatonokami Yasusada, a loyal and determined sword with a strong sense of duty, and Kashuu Kiyomitsu, his close companion who often provides emotional support. Other prominent characters include Heshikiri Hasebe, the citadel's strict but caring leader, and Mikazuki Munechika, an ancient and wise sword who offers guidance to the younger warriors. Each character embodies the traits of their historical counterparts, adding depth to their interactions and personal arcs.

The series balances action and slice-of-life elements, with battles against the Time Retrograde Army providing tension and excitement, while the quieter moments at the citadel explore themes of friendship, loyalty, and the weight of history. The seasonal backdrop of "Setsugetsuka" adds a layer of symbolism, reflecting the passage of time and the transient nature of life, which resonates with the characters' roles as protectors of history. The narrative maintains a lighthearted tone overall, but it occasionally delves into more serious and introspective themes, particularly when addressing the characters' pasts and the historical events they are sworn to protect.