By the time The Big O aired at the turn of the millenium, despite multiple upheavals in the mecha genre there were a fair number of unwritten rules in place. The mecha appears in the first episode, because that's how the toys are sold. As of Mazinger Z the pilot goes inside the robot, even if it's a so-called Super Robot that isn't weighed down by logistics or the possibility of being damaged. As a longstanding tradition those Super Robots worked well as colossal hulks, impractical from a realistic physics standpoint but imposing in both size and design. A few years prior Neon Genesis Evangelion showed that religion, especially Christianity, makes robot shows way cooler. Of course the pilot is a teenager, usually without any experience piloting a robot, and their mecha is the mouthpiece through which they convey their feelings and morality, arbitrating the forces of good an evil.
The first shots of The Big O are quiet looks at the city of Paradigm, where everyone keeps their head down and construction plates lie in the street. A sleek black limousine rolls down the street and somber jazz plays, as the negotiator Roger Smith, decked out in a black suit and impenetrable shades, introduces himself to us curtly the way a private eye would, saying “I perform a much-needed service here in this city of amnesia”. After a few more views of the city, a place that seems frozen in time, we see him double-crossed in a hostage trade only to double-cross the kidnappers right back, as well as the client who hired him to mediate the trade. He's not a starry-eyed teenager, much less a moral entity; he is an arbiter outside of justice, a womanizer with a butler and a mansion under his control, in a city where crime is almost as monotonous as every other piece of daily life.
The genre then is not immediately mecha, but noir. Even as we learn more about Paradigm and Roger's work within it, the feeling is distinctly that of film noir. Yes, the city has androids, artificial domes, and the occasional giant robot (called “Megadeus”; they did take some notes from Evangelion after all). There are aspects of the supernatural, such as the mass collective amnesia after a nameless catastrophe 40 years ago, or the existence of memories from before the incident existing somewhere in the world, in some shape that we never quite learn. We see the titular robot in the first episode, a hulking mass controlled from inside the chest by Roger. But for the first half all of the show these aspects simply set the stage, more of a homage to the fantastical worlds of mecha that came before. The core image still lies with a man in a black suit and shades driving through the dusty streets of a city defined by shadows.
More clear than the inspiration from past Sunrise shows is the Western component; one comparison that gets drawn a lot is with Batman. Roger plays the eclectic millionaire vigilante—although his face and job are well-known to the police—with his faithful and wizened butler Norman and gruff police chief Major Dustin. We meet the femme fatale Angel Rosewater, an agent who seems to appear in everything from the most hush-hush covert operations to being the secretary to Paradigm's president. Roger's enemies range from mad scientists to kidnappers, while his clients range from the salt-of-the-earth folks scraping out a living in Paradigm to the corrupt upper class. The lighting is dim, the character designs more rounded with heavy outlines save for the bottoms of the eyes, and color blocks being well-defined rather than blending into one another. The staff was practically built to do such an experiment, from scriptwriter Konaka Chiaki to sound director Tsuruoka Youta and headed by director Katayama Kazuyoshi and producer Maseba Yukata, who between them have covered innovative works from Cowboy Bebop to Serial Experiments Lain, both of whose influences are clear.
A minor point, more reminiscent of the Western superhero than the Japanese mecha: in order to punch with Big O, Roger physically pulls a lever rapidly along a arched track as if he were punching the enemy directly. While the mecha often represents a layer of separation between the protagonist and their faceless enemies, Big O seems to directly connect Roger to the opposing mechas. The show takes a monster of the week approach, but early on at least the enemy is often the mecha itself, rather than the person we presume to be inside.
This isn't to say the show can be entirely projected by combining landmark mecha and experimental anime with a Western take on noir and superpowers. One character who greatly stands out is Dorothy, the kidnapping victim in the first episode and a highly functional cyborg. Beyond pale skin and highly angled design is her expressionless face and tone of voice, all of which emphasize her robotic self, but her dynamic with Roger even from the start is the most vibrant part of the show. We see some anime tropes in her unintentional dry wisecracks, but she also picks up completely unexpected habits like playing rapid etudes on the piano to get Roger out of bed, which later turns into her hobby as another robot teaches her how to play less mechanically. And her frank dialogue spares us both any overwrought mental exercises on the nature of being human, and any restraint in giving both gratitude and frank advice to her employer. She also counters the well-trained Norman by only begrudgingly accepting Roger's two rules of the house: everyone wears black, and only ladies can come in uninvited.
The other big departure from Western tropes is in the second half, when religious elements and the overarching plot of Paradigm City get railroaded to the forefront in a crazy race to resolution and higher truth. I feel that here's where The Big O loses some of its magic, trading the stylistic elements for a breakneck pace and confusing its earlier lack of central plot for the lack of a goal or theme, ultimately trading focus for development. There are still plenty of great stories sprinkled throughout, and some much-needed development for the enigmatic Angel, but there are also episodes that fall flat or just feel plain weird. A strong cast all rises to the forefront, but that same cast worked just as well on a rotating basis, with antagonists falling back behind the veil for episodes at a time rather than being bold about their intentions.
The Big O was one of the legendary late-night adult-themed shows that aired on the Toonami block in the west, and has achieved a cult following similar to Cowboy Bebop (albeit much smaller) and Outlaw Star. Nestled right in the anime cult-hit sweetspot of the late 90's and early 2000's between the similarly atmospheric Lain and Texhnolyze, it aired at the same time two other Sunrise experiments, Taniguchi Gorou's directorial debut Infinite Ryvius and Tomino Yoshiyuki's personal Turn-A Gundam. All three riffed on many of the standards set two decades earlier in Mobile Suit Gundam, and in particular all three had unusual soundtracks that set the tone for vastly different viewing experiences than one would be used to going into a mecha, space, or Gundam show. Of the three, The Big O is perhaps the most well-known and certainly the most enigmatic, with a visual and directorial style that is rarely seen nowadays and a sense of emptiness that in my opinion flourished most during that brief five or six year window. I found it a bit harder to watch and fully immerse myself in towards the end, but the first half is certainly a must-see for fans of anime history, and in fact I would imagine it would be a great gateway show for Western fans looking to explore a more mature setting in anime.