Nagisa Natsunagi is a secondary main heroine and one of the central characters in the series The Detective Is Already Dead. She is an eighteen-year-old high school student with long black hair and red eyes. Her childhood was marked by a severe heart condition that left her physically weak and confined to a hospital bed for much of her early years, preventing her from attending school or living a normal life. One year before meeting the protagonist Kimihiko Kimizuka, Nagisa received a heart transplant from an unknown donor, which was later revealed to be the legendary detective Siesta. This transplant not only saved her life but also granted her a connection to Siesta, including the inheritance of one of Siesta’s Seven Tools: a musket gun.

Personality-wise, Nagisa is portrayed as confident and self-assured, often displaying a strong-willed and determined demeanor. Despite her past fragility, she possesses a resilient spirit and a hidden strength that emerges as she becomes more involved in the events surrounding Siesta’s legacy. She can be assertive and direct, though she also harbors a vulnerable side tied to her health history and her desire to live a full life. Her primary motivation is to find the person she sought Kimihiko to locate, a quest that ties directly to Siesta and the mysteries left behind. She also wishes to make the most of her second chance at life, embracing experiences she was previously denied.

In the story, Nagisa serves as Kimihiko’s first client after Siesta’s death, hiring him to help find someone. She quickly becomes a close ally and partner, often accompanying him on investigations and confronting dangerous situations. Her role evolves from a client into a key combatant and companion, using the inherited musket in battle. She demonstrates strategic thinking and adaptability, honing her abilities as she gains experience. Her relationship with Kimihiko is one of mutual trust and growing affection, as they rely on each other for support. Her bond with Siesta is profound, as the heart transplant forms a literal and symbolic link between them; she carries Siesta’s will and power into the present.

Nagisa also forms connections with other characters such as Charlotte Arisaka Anderson and Yui Saikawa, becoming part of a wider group that contends with supernatural and criminal threats. Her development is marked by her transition from a frail, isolated girl into a capable fighter and a confident young woman who actively shapes her own destiny. Notable abilities include her proficiency with the musket, which she uses for long-range attacks, and her growing combat prowess. Her heart condition, while largely mitigated after the transplant, sometimes serves as a reminder of her past and a source of emotional depth. Overall, Nagisa Natsunagi is a character defined by resilience, inherited legacy, and the pursuit of a meaningful life after hardship.