TV-Series
Description
Nagisa Natsunagi, an 18-year-old high school student, became Kimihiko Kimizuka's first client following Siesta's death, seeking his help to locate someone. Her childhood was marked by a severe heart condition and physical fragility, confining her to a hospital bed within an orphanage later revealed as a SPES experiment facility. Approximately one year prior to meeting Kimihiko, she received a heart transplant from an unknown donor, subsequently identified as Siesta. This procedure transferred not only Siesta's heart but also fragmented consciousness and one of her "Seven Tools," a musket gun.

Her appearance features hip-length black hair tied in a short tail on the right side with a red ribbon, ombre tips, and bangs framing her forehead, complemented by red-brown eyes. She exhibits a strong-willed, dominant personality, frequently using the phrase "Die Twice." After her transplant, subconscious urges, possibly influenced by residual memories or emotions from Siesta's heart, drove her to locate Kimihiko. This compulsion stemmed from a desire to uncover her donor's identity and understand the unexplained feelings tied to the organ.

The transplant also transferred supernatural abilities: "Hel's red eyes," granting Nagisa the power to exert control over other bodies at will. This power originated from Siesta's archenemy, Hel, whose consciousness had coexisted with Alicia before the transplant. Following the surgery, Hel's consciousness—alongside Alicia's suppressed personality—resided within Nagisa's body. Siesta's consciousness intermittently asserted control during critical situations to aid others. This dynamic positioned Nagisa as a vessel for multiple entities, though she gradually developed her own distinct identity.

Her background involved prolonged social isolation due to her health, leaving her without clear life goals upon recovery. This manifested as a persistent search for purpose, leading her to embrace investigative work alongside Kimihiko despite lacking Siesta's detective skills. Her development focused on reconciling her identity with the inherited legacies within her, striving for normalcy while navigating her dual consciousness. A spin-off light novel, *Natsunagi Nagisa wa Mada, Joshikosei de Itai* ("Nagisa Natsunagi Still Wants to Be a High School Girl"), explores her aspiration for an ordinary school life, depicting her forming friendships and investigating local mysteries with peers. This endeavor reflects her lingering curiosity about her heart's origins as she attempts to balance normalcy with her supernatural ties.

Her character arc culminates in a confrontation with SPES operatives where Siesta temporarily reasserts control over Nagisa's body to protect Kimihiko, confirming Nagisa's physiological and metaphysical connection to both Siesta and Hel and framing her existence as a fusion of multiple identities. Throughout subsequent events, she evolves from a figure defined by external influences into an active participant confronting the organizations intertwined with her past.