Of all of the anime titles that I have seen in recent years, few have cried out as loudly to be marathoned as this Winter 2020 series does. That is not because the series is so fiercely compelling (although it can be at times) or flows along so swiftly, but rather because its mind-bending structure and plot progression require intense, continuous concentration to sort out what is really going on. For better or worse, this is not light viewing.

The science involved here is wonky to the point that it might as well be magic: special psychic particles found at murder scenes can, when collected and transferred to a device called a Mizuhaname, allow for the construction of an “id well” of the killer, which can then be dived into using a VR-like console chair by someone who has killed themselves. (The latter fact is not apparent until the end of the second episode, however.) This is “black box” tech whose workings are not even understood by the handlers themselves. One revelation towards the end of the series partly explains why the tech is so obtuse, but even with that factored in the tech stretches the level of credibility.

The premise – about essentially entering the subconscious of a killer– has some parallels to the 2000 live-action movie The Cell, with a taste of Silence of the Lambs thrown in for good measure. Everything seen within an id well has symbolic or literal meaning, and these clues can be pieced together by outside observers to help locate serial killers and their victims. While these id wells are always to some degree abstract, they are also grounded in some form of logic, whether it be the world where everything (including people) are in pieces, a cityscape of charred bodies dominated by an inferno, or a desolate world scattered with massive drill bits. Coming to understand the logic of the setting is often critical to figuring out the killer, and that is usually the most fascinating aspect of these cases. Exactly why the girl Kaeru shows up as a murder victim each time is unclear until late in the series, and even then viewers have to extrapolate it rather than having it laid out for them, but it is connected to the bigger plot structure at work behind everything.

This is not a “case of the week” situation, however. Everything is at least vaguely linked, including Akihito's own past and how he got to the point of being a killer. A young, new detective named Hondomachi also gets deeply involved, first as a victim who uses one of the most audacious actions ever to clue her compatriots in about her location and then later as a different Great Detective in her own id well dive. Things get even more complicated when dives within dives start happening, and going into one's own id well can have interesting consequences. Keeping straight what layer of reality everyone is operating on can be as much a challenge for the viewer as for the characters.

Having serial killers as a topic naturally means that the content can get quite dark. Though the camera rarely lingers on the most disturbing imagery, some of the victims suffered quite gruesome deaths, including cases of limbs twisted off or one girl who gives new meaning to the phrase “beat to death.” (In context, this may be the most disturbing case.) Kaeru's deaths are usually not as graphic, but that is only by comparison; she is stabbed to death, hung, burnt, suffocated, and other nastiness, which has some ugly implications about the psychology behind why she is appearing that way. If you cannot normally handle Mature Audiences-rated detective shows, you should not watch this.

As neat as the series can be conceptually, it has two major flaws that limit its overall impact. The lesser of the two is the tenuous logic that John Walker operates under when it is finally revealed near the end of the series. Even if warped thinking is accounted for, it still feels like a stretch. The much more damaging and pervasive problem is thin characterizations across the board. With Akihito and Hondomachi, this is partly a product of the setting design, as the disconnect between the Great Detective and the original person in the real world also creates a characterization disconnect; a bit of their personality carries over, but they are almost two different people. The supporting cast is even more problematic, with only a couple of characters even getting firmly-established attitudes, much less personalities. The bulk of the support team, despite its members being named, are just there. This is rather surprising, as director Ei Aoki has proven well-capable of managing large casts in previous efforts like Re:CREATORS, Aldnoah.Zero, and Fate/Zero, but even describing some of these characters by anything more than what role they play would be difficult.

The production effort fares better, though it can also be hit-or-miss. Studio NAZ had an ambitious visual production to deal with here; just handling the first two episodes, where people have missing parts and a whole town is essentially floating around in chunks, had to be challenging, but the heavy use of CG works especially well here by lending an extra layer of unreality to the fractured id well. That is not the only visually impressive id well, either; the inferno scene, with its shifting and growing buildings, also dazzled. Genuine action scenes are few and far between, but one in the middle of the series proves that a fight between a boxer and someone wielding a handgun can be quite dynamic. On the downside, animation in the regular-world scenes sometimes falters, especially in the middle episodes. Graphic content, as noted before, can be extreme.

The audio side maintains a more consistent level of quality. Kisuke Koizumi has had a substantial career as a sound director, but here he forays into music direction for the first time. The resulting musical score leans heavily on electronica and effectively generates a sense of both tension and mystery in doing so. The score also uses a broad collection of insert songs, some more effectively than others. Opener “Mister Fixer” is an energetic adult contemporary-styled number, while the hard edge and heavy electronic beat of closer “Other Side” makes more of an impression.

Funimation provides the English dub, anchored by Josh Grelle as Sakaido/Akihito and Monica Rial as Hondomachi. Both fit the roles well, but the entire dub has a bit of a flat sound. In fairness, this could be the fault of the series, as few of the characters have much expressiveness to their normal deliveries; about the only two who escape this are Akihito's daughter Muku and field analyst (and Handomachi's senior) Matsuoka.

The Blu-Ray/DVD release of the series comes in both a normal and Limited Edition version. Both have a 39 minute long “Inside the Minds of the Staff and Cast” featurette, which is basically a Q&A session with Ei Aoki, character designer and animation director Atsushi Ikariya, and the seiyuu for Sakaido and Momoki; the most interesting details from that is that the project was 7-8 years in the making and was not originally planned as a mystery. The LE version comes in an artbox with a 120-page booklet and an extra box of goodies. The first 97 pages of the booklet are a collection of character art, background art, key frames, and illustrations,while the last 20 or so pages are a short story from Akihito's point of view where he reminisces on his family. The box contains art card of the three Great Detectives and their real-world counterparts and an acrylic standee of Sakaido. If you're a big fan of the series, forking out the extra for the LE version is probably worth it.

The series as a whole is worth the time for its mix of mystery and sci-fi elements and the dark, complicated mind trip it takes the viewer along. However, some questionable twists towards the end keep it from being a stand-out effort.