WARNING: The following contains spoilers for Episode 4 of The Detective Is Already Dead, "What I See in That Eye," now streaming on Funimation.
Little has been revealed about world-class detective Siesta since her sole appearance as the protagonist in The Detective Is Already Dead Episode 1. In that episode, it was revealed that she used the name "Siesta" as an alias and that she was highly skilled at preparing for her cases in advance, similar to DC Comics' Batman. This was how she was able to recruit protagonist Kimihiko Kimizuka as her unwilling sidekick.
Siesta also carried around a special gun that she tailored to detect her DNA and was known to be homeless, bunking wherever she could. At one point, she even stayed with Kimihiko in his apartment where she also showcased her lack of respect for personal boundaries and her love of pizza. Since then, details of Siesta's past have been revealed sporadically.
In Episode 2, it was revealed Siesta had passed away the previous year and that she had donated her organs. Her heart went to Nagisa Natsunagi, who has since taken over Siesta's role as a detective. In Episode 4, a post-credit scene introduced the newest main cast member, Charlotte "Char" Arisaka Anderson, who is surprisingly revealed to have known Siesta while she was still alive.
In the few minutes that she is given, a lot is revealed about Char, beginning with the fact she originally functioned as Siesta's muscle. Unlike Kimihiko, Siesta never treated Char as a sidekick, but instead established a different kind of relationship with her: a mother-daughter-style relationship. This is best evidenced in the yacht scene where Char calls Siesta "mom" and curls up on her lap for comfort. The relationship seems to hint at Char's emotional immaturity, which creates something of a power imbalance between her and Siesta -- a power imbalance Siesta seems to nurture.
Another thing that's revealed about Char is that she doesn't like working with Kimihiko, expressing her preference to work alone. This seems to hint at a rivalry between them. It is unknown for how long Char knew Siesta or if she even came before Kimihiko. At best, the locket at the start of the post-credit scene seems to hint at a lengthier history with Siesta and Char may have already been working alongside her prior to Siesta's meeting Kimihiko in Episode 1.
The most significant detail that's revealed about Char in the post-credit scene, however, is the fact she was present on the day Siesta died. Siesta even further hints she recruited Kimihiko to work with Char because she knew she was going to die soon and needed successors to continue her work in the future. As such, she purposely got a “dim-witted” girl who could fight alongside a “clever boy" who with no fight in him to compensate for each other’s weaknesses and become a stronger unit.
While Char's history with Siesta should be revealed in upcoming episodes, the few details that have been established in Episode 4 seem to be building on developments first established in Episode 1. Specifically, it seems to be building on the reason Siesta died and seems to be setting up for a major reveal of Siesta's posthumous plans.
