WARNING: The following contains spoilers for Episode 2 of The Detective Is Already Dead, "I Still Remember, After All This Time," now streaming on Funimation.
The Detective Is Already Dead revealed at the end of Episode 1 that Siesta is dead and that the entire first episode was a flashback to Kimihiko’s first adventure with her. Episode 2 confirms Siesta's fate but also drops hints that we haven't seen the last of her. The way the episode plays around with Siesta's posthumous presence is both clever and a bit surprising.
The first hint about Siesta's presence in Episode 2 comes with the introduction of a new character: Nagisa Natsunagi. Though a total stranger to Kimihiko, she has nonetheless been following all his cases in the three years he was working as Siesta's sidekick. When the two characters meet for the first time, Nagisa shows Kimihiko a series of headlines of cases he has worked on, but none of the news articles mention Siesta. As such, Nagisa believes Kimihiko is a teenage sleuth, which surprises him.
With the news coverage, it is strongly implied Siesta may not have actually been real. Given the way Episode 1 of The Detective Is Already Dead played out, Episode 2 teases the possibility Siesta may have been a figment of Kimihiko’s imagination when he was in a vulnerable place in his life. He may have been the “legendary detective” solving cases all along, and Siesta may have “passed away” once he got into high school and no longer needed her. This makes perfect sense when taking into account how Kimihiko demonstrates his own deductive reasoning when Nagisa asks him to investigate the identity of her own heart donor. But just as quickly as the episode proposes the idea of Siesta not being real, her existence is confirmed by both assistant police inspector, Fuubi Kase, and the villain of the previous episode, Bat (Koumori).
Throughout the episode, Nagisa reports experiencing cellular memory transference from her heart donor, which causes her to obsess over her donor's identity. This brings her and Kimihiko to Fuubi, who in turn, gives them access to Bat's holding cell in the maximum-security prison. They believe that, given Bat's unique abilities as a cyborg, he might be able to identify the original owner of Nagisa's new heart. It's immediately established he can hear different heartbeats from hundreds of kilometers away and can easily identify people by the distinct sound of their hearts. When he greets both Kimihiko (whom he identifies as "Watson" from the previous episode) and Nagisa for the first time, he also greets "the legendary detective," which Kimihiko thinks is in reference to himself.
The buildup in this sequence in The Detective Is Already Dead is quite brilliant because the longer Bat interacts with Kimihiko and Nagisa, the more it becomes increasingly obvious who Nagisa's heart donor actually is. By the time Bat reveals the identity of the donor as Siesta, the viewer would've already made that deduction themselves, and Bat's method of confirmation ends up recalling his first encounter with Siesta in Episode 1. The reveal, however, does more than just confirm the identity of Nagisa's heart donor.
The revelation of Siesta's heart residing within Nagisa actually builds on Siesta's habit of preparing for her cases in advance, which means she knew at some point she was going to die. This does two things: first, it establishes the danger threshold of Siesta's enemies, which helps validate Siesta's reputation as a world-class detective. The second thing it establishes is that Siesta became an organ donor as a way of cheating death. This actually explains Nagisa's obsession with wanting to identify her heart donor, but more importantly, it also explains why Nagisa started displaying some of Siesta's personality traits. It also explains why she behaved as though she knew Kimihiko, despite being a total stranger to her, which in Japan, is considered rude -- something both characters acknowledge earlier in the episode.
With Siesta being established as an organ donor, it's probably safe to assume future members of Kimihiko's team will also be recipients of Siesta's other organs. This will effectively allow Siesta to continue to have a presence in the anime without giving Siesta a full comic book-style resurrection.
