Chizuru Yukimura, a determined young woman from Edo, ventures to Kyoto on a quest to find her missing father, Kodo Yukimura—a physician pioneering Western medicine. Her search draws her into the orbit of the Shinsengumi after surviving an assault by Furies, berserkers twisted by the Water of Life, an elixir her father formulated under shogunate mandate. Mistaken for a boy in her disguise, she is detained by the group, only for them to uncover her identity and ties to the elixir’s origins.

As an aide to the Shinsengumi, Chizuru navigates the volatile political landscape of 1860s Japan, forging tentative alliances with its members. Her resolve is tested during a covert operation in Shimabara, where she infiltrates the geisha world to expose samurai conspiring against the group. The mission, interwoven through shifting viewpoints, showcases her espionage skills and strategic rapport with the captains, though she remains more observer than combatant.

A startling revelation unveils her demonic ancestry, connecting her to oni clans who assert her father’s elixir experiments sought to breed Furies as tools of human subjugation. This heritage thrusts her into clashes between the Shinsengumi, rival demon factions, and power-hungry forces vying for the elixir. Despite dormant powers tied to her lineage, her journey prioritizes her analytical perspective and supportive contributions, dissecting allies’ motivations amid chaos.

Her bond with the Shinsengumi shifts from pragmatic alliance to forged loyalty, particularly with figures like Toshizo Hijikata, as she confronts their sacrifices and the gray morality of their cause. Chizuru grapples with her father’s legacy and dual heritage, her choices mirroring the era’s collision of history and myth, even as her agency remains entangled in the supernatural and political storms engulfing Kyoto.