WARNING: The following contains spoilers for Episode 9 of The Detective Is Already Dead, "SPES," now streaming on Funimation.
The Detective Is Already Dead has spent the last four episodes detailing Kimihiko Kimizuka's last case with Siesta leading up to the latter's death. In those four episodes, viewers were treated to more of Kimihiko and Siesta's fun dynamic as they investigated SPES activities in London, England. Siesta even revealed her more vulnerable side when she and Kimihiko drank alcohol for the first time, leading up to a not-so-fondly remembered night together in Siesta's bed. All this buildup just to crush every viewer's heart when the moment came to reveal what truly happened to Siesta on the fateful day she lost her life in Episode 9.
Picking up where Episode 8 left off, Siesta, Kimihiko and Charlotte Arisaka Anderson (aka Charl) are on a boat making their way to an island to defeat Hel and recover Alicia. The latter is actually one of Hel's Dissociative Identity Disorder alter egos. Charl and Kimihiko go to the SPES base to fight Chameleon, who turns out to be an extraterrestrial plant known as SEED, the true leader of SPES. SEED's true objective is to terraform the Earth and reproduce, killing every living thing in the process. While Charl fends him off, Kimihiko goes to assist Siesta in her battle with Hel.
During their fight, Hel reveals to Siesta that Alicia is the real personality. Sometime after SEED arrived on Earth, he abducted Alicia and carried out torturous experiments on her body, traumatizing her. This in turn caused Alicia to develop the non-binary Hel personality, presumably to protect her from the horrors she experienced. Hel, however, chose to embrace SEED's villainous mission and tortured Alicia themselves. Siesta deduces that Hel is actually driven by a need for love from a father figure, which angers them, validating Siesta's deduction. The fight, however, turns deadly when a monster Hel previously controlled runs loose, resulting in Siesta losing consciousness and Hel killing the monster. This wears out Hel's transplanted heart, and they proceed to replace it with the heart of the unconscious Siesta, killing her in the process.
This reveal in The Detective Is Already Dead does a lot more than show the events that resulted in Siesta's death. It actually has significant implications as to the true identity of Nagisa Natsunagi, the current host of Siesta's heart. In fact, the episode seems to confirm that Hel and Nagisa are one and the same. To start with, they have a similar appearance, with Nagisa looking like Hel with longer hair. Nagisa has also demonstrated she has gaps in her memory (like not remembering who her heart donor is), which is a symptom of Dissociative Identity Disorder.
Furthermore, the Nagisa personality may have been born out of both Siesta's and Alicia's personalities, as she has traits of both. The final touch is the red ribbon Nagisa wears in her hair. It's the same ribbon Siesta wore in her hair during the Toilet no Hanako-san case, and it's the same one she promised to give to Alicia in London.
The last thing that's significant about The Detective Is Already Dead's flashback story arc's conclusion is that it proves to be an important episode for both Siesta and Kimihiko. Since the start of the episode, Siesta consistently hinted that she knew she was going to die and tried to say goodbye to Kimihiko the only way she knew how. Prior to the fight with Hel, Siesta wanted to hug Kimihiko but he declined. She also wanted to tell him how she truly felt about him but he refused to hear her out. It's not until Hel succeeds at killing Siesta that Kimihiko finally breaks down and admits he always loved Siesta and regrets not expressing this when he had the chance.
In many ways, Episode 9 was always going to be a heartbreaking episode to watch. Not only does it finally reveal how Siesta truly died, but it even validates the romantic attraction that always existed between her and Kimihiko, making her death all the more devastating. With the revelation that Hel and Nagisa may be one and the same, the reality of this is going to gravely impact Nagisa's relationship with Kimihiko moving forward, especially given Kimihiko's own feelings for Siesta.
