"Hakuōki Sekkaroku" is a manga series that serves as a spin-off of the larger "Hakuōki" franchise, which is based on the historical Shinsengumi, a special police force active during the Bakumatsu period in Japan. The story is set in Kyoto during the late Edo period, a time of political turmoil and social upheaval as the Tokugawa shogunate faces decline. The narrative intertwines historical events with supernatural elements, focusing on the Shinsengumi and their interactions with a young woman named Chizuru Yukimura.

Chizuru Yukimura, the protagonist, is the daughter of a doctor who has gone missing in Kyoto. Determined to find her father, she disguises herself as a man and ventures into the city. Her search leads her to cross paths with the Shinsengumi, a group of elite swordsmen tasked with maintaining order in Kyoto. Initially mistaken for a spy, Chizuru is taken into custody by the Shinsengumi. However, her knowledge of her father's work and her connection to the mysterious "Water of Life," a substance that grants supernatural abilities, make her valuable to the group. As a result, she is allowed to stay with them under their protection.

The Shinsengumi members, including the stoic and disciplined commander Toshizō Hijikata, the charismatic and skilled swordsman Sōji Okita, and the calm and strategic Isami Kondō, play central roles in the story. Each character is portrayed with distinct personalities and motivations, reflecting their historical counterparts while incorporating fictionalized traits. The group is embroiled in conflicts with rival factions, such as the Ishin Shishi, who seek to overthrow the shogunate, as well as supernatural threats tied to the Water of Life. This substance, while granting immense power, comes at a cost, transforming its users into monstrous beings known as Rasetsu.

As Chizuru becomes more deeply involved with the Shinsengumi, she uncovers secrets about her father's research and the true nature of the Water of Life. Her presence also influences the dynamics within the group, as her compassion and determination earn their trust and respect. The story explores themes of loyalty, sacrifice, and the moral complexities of wielding power, set against the backdrop of a nation in transition. The interplay between historical events and supernatural elements creates a compelling narrative that balances action, drama, and emotional depth.