The animators never started caring, while the writing's like the stories you wrote when you were twelve. That's not hyperbole, by the way. There's nothing to the cast beyond their one-line descriptions, while the story is basically an attempt to be cool with violence. Unfortunately it involves empty characters in an empty setting, but... hey, monsters!
That said, though, it's not as terrible as everyone says. It's watchable in an empty, pointless sort of way, once you've accepted that the animation is in the toilet.
Firstly, it's Chinese. Its heroes are Chinese, the theme song's in Chinese and it's based on a Chinese webcomic called Time Prisoners. It's just the animation that was made in Japan. There was a rash of Chinese-Japanese anime co-productions in 2016 and apparently this is one of the best of them. Yikes. Its animation looks so cheap that it's impossible not to start wondering about reasons why. Did it have no budget? Alternatively, did the Chinese producers annoy the Japanese studio? After all, Japan's anime industry is based on everyone working insane hours and killing themselves to get the work finished. Sometimes they burn out, or even commit suicide. They're not doing it for the money. The pay's famously bad. They're doing it for love... so if the Chinese studio managed to annoy the Japanese one, maybe that might have made everyone more inclined to allow themselves some work-life balance?
Is this what anime would look like if everyone in the industry was sane? Who knows? Well, I'm speculating. I'm just making stuff up with no evidence beyond the fact that this show looks horribly cheap. It's not even a fun kind of badness. It looks boring. It's the kind of simplicity that suggests that the animators are drawing as little as they can get away with. Usually it's just cheap, but sometimes the draftsmanship suffers. There are shots where faces don't look like faces.
As for the lines, they're drab. It's like watching a rough cut. You'll have the outlines of things and not necessarily much more than one or two disconnected construction lines within that to suggest form.
As for the story, it's about vampires who aren't called vampires. They're "bloodivores". This makes almost no difference to anything and there's no real story point to their vampirism, beyond justification for some nasty backstory. (Vampirism was an unexpected side-effect of a commercially licensed drug and the situation seems to be under control, but even so the government tried to exterminate them, started a civil war and eliminated an entire city.)
Our heroes are Nice-ish Boy, Token Girl With Big Boobs, One-Note Boy #1 and One-Note Boy #2. The first of those is unobtrusively in love with Token Boobs and the other is a bit of a bastard, but they're generic enough that you'll forget who they are if they're not tagging along with someone else. Later they'll also run into Professional Killer In Purple Coat, Arrogant Super-Strong Killer In Orange Coat and Untrustworthy Girl. That really is almost all there is to these characters and it's liable to make the show mildly soporific, in a "was I meant to be paying attention?" way. In their defence, though, the cast gets more watchable in later episodes. They're rudimentary types rather than characters, but they're still capable of acting in accordance with their motivations and doing significant things. At their best, they can be functional dramatic characters, on a basic level.
It would also be wrong not to acknowledge that the writing is capable in flashes of being actually good. The inhumanity of children and teachers in ep.3 is genuinely horrible, while there's pathos in the ep.6 material with Nice Boy and Token Boobs. Those were good bits. Unfortunately no one's going to notice because no one's going to care about a few isolated peaks in what's otherwise a featureless storytelling desert.
Oh, I forgot a character. There's Yaya. She's an animal-like little girl with a one-word vocabulary ("ya").
The plot starts with our heroes robbing a bank and making both that and themselves look boring. This gets knocked on the head by a government conspiracy or something. Soon our heroes have been condemned to death, apparently machine-gunned by an unofficial death squad and then locked in a warehouse with lots of other Death Row inmates and some really big monsters. This probably sounds promising. It's not. It's crushingly unimaginative. Aggressive, boring people in a featureless environment are being attacked by anonymous monsters for no reason. What's more, some of those people are good at killing! If you like action films, there's a chance that you might have a modest amount of fun watching this.
Later, the script throws in other stuff. There's something that the English subtitles call "hemomancy" and the Japanese dub calls "ketsu-nou" (blood power). This lets you turn into monsters, grow swords from your pores or whatever. The latter was wacky enough to entertain me briefly, but not as much as me pretending to myself that "ketsu" was really its alternative translation of "arse". There's also a character who spends most of ep.11 having apparently forgotten that he's impaled on a sword. He has normal conversations and shows no pain or discomfort. "Are you okay?" "Yes, I'm fine."
"It feels as if we've been caught up in an intersection of space-time." Really? That's a surprising thing for an ordinary person to conclude. For another example of magical knowledge, see "the counter increases every time you kill someone!"
Ep.5 also suggests that you can give a blood transfusion by having the victim drink it. This seems improbable to me, but I can't protest too much. They're vampires, after all.
This show is a complete failure by almost any standards. However that's not because it's horrible. It's not. It's sort of basically okay, if you don't mind super-cheap animation and utterly underwhelming writing. It's a solid, dependable three out of ten. It's just that it's the kind of bottom-feeding juvenalia that can only dream of attaining mediocrity. When I said it was like stories you wrote when you were twelve, that wasn't exaggeration.