WARNING: The following contains spoilers for The Detective Is Already Dead Season 1, now streaming on Funimation, and Vols. 1 and 2 of the light novel series, now on sale by Yen Press.
The Detective Is Already Dead (Tanmoshi) is a highly popular light novel series in Japan by author Nigojū with illustrations by Umibōzu. The first two volumes of the light novel series were adapted into a 12-episode anime that aired in both Japan and the US as part of the summer anime lineup.
While the anime adaptation follows the same central storyline as the first two light novels and makes very little alterations to the characters and dialogue, it makes significant changes in executing the plot. Additionally, when the content is translated into English, more deviations between the media arise, partly due to the different ways Japanese phrases can be translated and sometimes even because of mistranslation.
The Story Is Told in a Different Order
One of the major differences between the first two Tanmoshi light novels and the anime adaptation is the order in which the story is told. Vol. 1, for example, only contains the plot beats where protagonist Kimihiko Kimizuka meets Nagisa Natsunagi and Yui Saikawa for the first time. It also features the story where Kimihiko reunites with Charlotte Arisaka Anderson on a cruise ship, after one year apart. This is when Yui and Nagisa together meet and team up with Charlotte.
Siesta -- the titular dead detective -- is introduced in the prologue of Vol. 1, but is not featured prominently throughout the book. Her first meeting with Kimihiko is also not fleshed out in one go, as it is in the pilot episode of the anime. Instead, her team-up with Kimihiko is gradually revealed in the chapter where Nagisa meets Bat in prison to learn the identity of her heart donor, who turns out to be Siesta.
Similarly, the Toilet no Hanako-san case doesn't appear until Vol. 2 of the light novel series, along with the London story arc that was featured as a flashback mini-arc in the anime. This marks another major difference between the anime and light novel: both the Hanako-san case and London arc are presented as video footage Siesta posthumously put together for Kimihiko, Charlotte, Nagisa and Yui to view so that they learn the true circumstances of her death. This detail is omitted from the anime entirely.
The Anime Omits the Medusa Case
One of Siesta and Kimihiko's earlier cases is featured in Vol. 1, but is left out of the anime. This is the Medusa case, where they investigate a wealthy man's daughter who can seemingly turn people into stone. The chapter is significant as it hints at Siesta's origins and her connection to Yui Saikawa -- two details largely absent from the anime.
In the chapter, Siesta is implied to be one of Yui's fans and hums one of her popular songs. In the Japanese-language version of the light novel, Kimihiko asks Siesta about the song. She responds, "it's a Japanese idol song," but uses the English word for Japan instead of the Japanese word, saying, "Japan no aidoru songu." This actually marks the other significance of the chapter: it provides one major clue about Siesta's nationality.
Throughout Vols. 1 and 2, Siesta is described as having Caucasian features by Kimihiko, who describes himself as a pure Japanese person. The fact that Siesta watched a foreign drama on his TV during the Hanako-san case further validated his belief she may be of European descent. During the Medusa case, when he hears Siesta describe his home country as "Japan," this prompts him to ask her where she's from, implying she may be from an English-speaking country. Given that Siesta often subscribes to British stereotypes and makes British references, she's implied to be British in origin.
The One-Night Stand Differs
Another major difference between the light novel and anime adaptation is the depiction of Siesta and Kimihiko's one-night stand. In the anime, it's presented as a flashback sequence without context. The details of what actually happened are left ambiguous. Not only does the light novel more explicitly clarify the dalliance, but the one-night stand is better contextualized as well.
Since Vol. 2 established that Kimihiko's memories were compromised in the battle with SPES that sealed Siesta's fate, another reason Siesta posthumously created a video of their time together was to jog his memory. She actually included the one-night stand in her video, but purposely left out the details of their sexual activity, most likely to spare herself further embarrassment.
While the Japanese version of the light novel is clearer about what happened, the English translation by Yen Press ironically presents the sexual encounter as more ambiguous than it actually is. One major change is how Siesta confirms her sexual interest in Kimihiko in Vol. 1. In the Japanese light novel, Siesta says, "I see. To tell you the truth, at least once, I could consider sleeping with you." In the English translation, her line is changed to, "I see. To tell you the truth, I might have slept with you once. At least I considered it."
The aftermath of the one-night stand is also different between the original Japanese text and the English translation. While Kimihiko, in the Japanese version, describes the sexual encounter as "late-night tension" to convey the awkwardness of the whole experience, in the English translation, this is changed to "late-night moments of weakness." Kimihiko, in the Japanese text, additionally describes the sexual activity as "shameful behavior" (shuutai) whereas the English translation changes this to "sorry display."
Differences in Translation
On the subject of the English translation, there are more inconsistencies between the anime and light novel series. While the English translation of the light novel tries to be as accurate to the Japanese version as possible, the English subtitles for the anime take more liberties, most likely to match the English dub script. This is notable with the way recurring words and catchphrases are translated throughout the series.
Three commonly used terms in both the Japanese light novel and anime adaptation are "mei tantei" (great detective), "joshu" (assistant) and "jinzouningen" (artificial human). Yen Press translates these three terms as "ace detective," "assistant" and "pseudo-human," respectively, which are close to their actual Japanese meanings. The Funimation subtitles translate these terms as "legendary detective," "sidekick" and "android," respectively. While "android" is still a correct translation of "jinzouningen," the term is also a bit misleading since the jinzouningen in Tanmoshi are alien plant-and-human hybrids, which are fully organic. However, the term "android' implies "human on the outside, machine on the inside."
Another facet to note is the way Siesta, Kimihiko and Charlotte's catchphrases are translated. In Japanese, Kimihiko tends to describe his displeasure as "rifujin da," which can be translated as either "this is absurd" or "this is unreasonable." The first translation is the one Funimation goes with while Yen Press changes this to "not fair." Charlotte, in Japanese, refers to Siesta as "Ma'am" and is translated as such in the Yen Press version. Funimation incorrectly translates this as "mom." Relatedly, Charlotte's nickname of "Charl" is also translated differently between Funimation and Yen Press. The Funimation translation goes by "Charl," while the Yen Press translation changes her nickname to "Charlie."
Lastly, Siesta's Japanese catchphrase of "baka ka, kimi wa?" plays with the first kanji in both Kimihiko's family name and given name, which means "you." The actual translation of the phrase is "are you an idiot?" and, given the context, it also conveys "are you a moron, Kimi?" Yen Press translates Siesta's catchphrase as "are you stupid, Kimi?" to capture the pun, while Funimation simply translates it as "are you stupid?" While still correct, whether or not the viewer catches the pun is dependent on their Japanese language skills.