WARNING: The following contains spoilers for Episode 7 of The Detective Is Already Dead, "In Time, You Will Remember This Day," now streaming on Funimation.
The Detective Is Already Dead has been teasing a potential romance between protagonist Kimihiko Kimizuka and world-class detective Siesta since Episode 1. From the moment they posed as a married couple while investigating the Toliet no Hanako-san case in Japan to the time they investigated the Jack the Ripper case in England, the anime has been building romantic tension between the two. Three episodes into the latest flashback storyline, Episode 7 finally delivers what audiences have been waiting for.
It all started with Episode 5, when Siesta and Kimihiko were on holiday on a nice beach. During a boat ride in the ocean, a bikini-wearing Siesta began flirting with Kimihiko and even started checking out his body. At one point, she teased him about staring at her chest and went as far as to say that if he had any plans to reveal any feelings for her that he'd "better do it soon" as she was very "sought after."
During an encounter with SPES leader Hel in Episode 6, Siesta further hinted at her feelings for Kimihiko when she sat on his lap in a robot she was piloting and "warned" him not to take advantage of the situation. When she thought the fight with Hel would turn fatal, Siesta went out of her way to get Kimihiko to safety before launching a suicide attack against their adversary. She survived but was injured in the process. When Kimihiko showed concern for her after fearing losing her, she teased him with a marriage proposal when he turns 18.
Now in The Detective Is Already Dead Episode 7, things really start to take off. After two weeks of recovery, Siesta invites Kimihiko and Alice to dinner where she continues her flirting. Alice notices the other two behave a lot like a couple and even asks if they're romantically involved. Siesta silences her and manages to get her to go to bed early so she can drink alone with Kimihiko. Later in the evening, a very drunk Siesta in a bathrobe tells Kimihiko about a childhood memory she has and asks why he isn't sitting beside her. Kimihiko tries to establish boundaries, but she insists they get into bed together. A very reluctant Kimihiko complies.
The whole time they lie in bed together, Siesta (still drunk) begins admitting her feelings for Kimihiko, namely that she enjoyed their three years together. She starts caressing his cheek and reveals more of what she likes about him. Shortly after this, she begins making sexual advances toward Kimihiko and even suggests they "try something not so serious." Kimihiko is not oblivious to Siesta's intentions, and his suspicions are immediately validated when she proceeds to kiss him.
Exactly what went on between Siesta and Kimihiko that night is left to the viewer's imagination. The way both characters behave the next morning, however, more or less confirms a sexual encounter took place. Kimihiko (who was sober the whole time) feels ashamed about what he did and expresses a desire to die in a non-suicidal way. He feels even more embarrassed when Siesta wakes up next to him and he doesn't know how to explain the situation to her.
At first, Siesta doesn't seem to recollect what she did the night before -- until noticing her state of undress. After putting two and two together, Siesta begins to feel embarrassed at the possibility she may have acted on her sexual feelings for Kimihiko. Not wanting to live with the knowledge that her sidekick got to experience an intimate night with her, she attempts to erase his memory with the same drug she procured from the Toilet no Hanako case three years earlier. She is interrupted by Alice, who noticed a lot of noise coming from the room.
Now that The Detective Is Already Dead has given some confirmation about the nature of Kimihiko's past relationship with Siesta, it does a lot to contextualize his present interactions with Nagisa Natsunagi, who is now in possession of Siesta's heart. It also has significant implications for where his relationship with Nagisa could go given his romantic attachment to Siesta.