It's not very good, but I don't think the show cares about the way I mean that. Not only does it not care about being emotionally engaging, but I think it's deliberately avoiding it. The characters aren't meant to be likeable. It's an efficient exercise in grim adults-only unpleasantness with nudity and grotesque violence.
You see, the show's only problem is the fact that you don't really like or care about anyone, so the episodes grind past in a joyless way that should defeat any attempt at marathoning. Apart from that, it's solid. The show's mythology is multi-layered and complicated, the characters are distinctive, the multi-generational narrative is doing some interesting things and it's well drawn and animated.
It's about immortals. Rin, Mimi and their dog don't get old and never die. Even if you kill them, they'll just get better again. The backstory for this is borrowing from Greek (Mnemosyne), Norse (Yggdrasil) and Japanese (Tajimamori) mythology, to mention just the more significant borrowings. They also reference the legend of eating mermaid's flesh, while "Project L'Isle-Adam" in episode four is a reference to a 19th century French symbolist writer whose output included what sounds like SF to me. You see, in the world of this anime, there's a world-tree (Yggdrasil) that keeps shedding Time Fruits. If a woman eats one of these, she becomes immortal. If a man eats one, though, he'll become a bestial "Angel" with a life expectancy of about a fortnight, who lives only to hunt down, have sex with and devour immortal women. The latter will be overcome with lust and unable to resist an Angel's amorous attentions, even if they know it'll mean their own deaths.
Anyway, Rin runs a one-woman detective agency, with Mimi as back-up in the office. (Mimi's a computer whiz, but Rin's the one who can kill people with her bare hands.) Well, why not? What else have they got to do? It's as good a way as any of keeping yourself busy. Rin has mortal contacts, none of whom like her much, while her enemies include a remarkably persistent assassin and a demigod called Eipos whose hobbies include having immortal women skewered slowly on a hundred swords.
Rin doesn't like running, perhaps because of her bust size. She'll be doing plenty of it, though, not always fully clothed.
Theoretically, this should be quite a well-made show. The episodes have interesting ideas, some depraved villains and a mythology that if anything is a bit too complicated. Episode six got a bit abstract and "if you say so", at least as far as I was concerned. It's not that I didn't understand it. I just didn't really connect with it, because it hadn't been set up well enough for me to find it dramatically meaningful.
Above all, they're turning their backs on the link between character and action. Almost until the end, Rin has no personal stake in anything. She can't be killed. She's just taking on random cases and investigating whatever takes her fancy at the time. She's not even particularly likeable, but fortunately she's extremely good at what she does (e.g. killing baddies who can't kill her) and basically on the side of good. That's why we don't turn off, even if a more dramatically engaged lead character might have made us actually want to watch the following episode too.
Mimi is more likeable, but she doesn't get involved in field operations (until episode six) and she too is basically doing this to pass the time.
Rin's allies are almost all dull and uninvolving. Koki Maeno is such a personality void that he's like a Brechtian experiment in alienation. I ended up being quite fond of the grumpy policeman, though.
Almost everyone dies, though. That's the point. What else are you going to do for dramatic contrast in a show where the lead character's immortal? After a while, mind you, even the immortals are getting killed. (The show does cheat, though.)
My favourite thing about the show is how it uses time. Its episodes take place in 1990, 1991, 2011, 2025 and 2055, plus flashbacks (sometimes going back a long way). Characters can be children or even grandchildren of earlier allies. The early episodes are set at a time when the Soviet Union can still be the bad guys, but then the futuristic episodes get into SF extrapolation and VR/cyberspace tech. It has ideas like the concept of a crime witness being quite a complicated affair in a VR-saturated future. (What's more, it does all that twice over. This show has two futuristic eras, not one, with 2055 obviously being more advanced than 2025.)
I should address the adults-only content. The violence is brutal and sometimes grotesque, while I'm sure some people would argue that the sex and nudity are pushing this towards pornography. It's not, but that's due to the tone. It's so dour and unrelenting that you'd have to be mentally disturbed to regard this as whack mag material. Mind you, I admire whoever thought up a phallic tower of moaning naked zombie women. That's like Freud cubed. Incidentally, this show was commissioned for the tenth anniversary of the Japanese cable channel AT-X, which is known for showing late-night animated sleaze.
Oh, and don't be fooled by the fact that it only has six episodes. They're double-length, making this the equivalent of a twelve-part series.
I couldn't call this an enjoyable show, I'm afraid. I'd been expecting to zoom through, but it's too much of a slog for that. It's not even getting full value from its gore, because you don't make enough emotional connection to be shocked. However it's also cool, stylish and good at what it does. The action is strong, it builds plenty of atmosphere and it's quite interesting to think about, with a pleasingly thorough and wide-ranging exploration of its ideas. Plus, y'know, boobs. The show looks good and I'm sure it has lots of fans. If you stumbled upon a random episode out of context one day, you might even be impressed.