Its weakness is that it's based on a light novel series. However it's also dark, sincere and has some twisted worldbuilding. I liked it a fair bit.
Melida Angel is the 13-year-old daughter of the aristocratic Angel family, but she doesn't seem to have inherited their magical abilities and Paladin character class. Her paternity is in question. If she really is illegitimate, the duke wants her assassinated. (You'd think he could have just had a DNA test, since this world has advanced genetic engineering, but maybe he's pathological about wanting to keep his doubts private.)
Kufa Vampir is the assassin. Melida thinks he's her private tutor, which technically he is also. In ep.1, he can hardly bear to watch Melida working so hard at her training to join the elite Crest Legion. She's obviously a nobody. She's clever, but powerless. She's never going to achieve the goals she's so desperately pushing herself to achieve. Murder would be an act of mercy.
Then, though, he changes his mind. He decides that she's worth training. He even shares some of his own mana with her, to compensate for her innate lack of it. This makes the show a lot less dark, since one of our heroes is no longer trying to kill the other, but it's still hardly rainbows and butterflies.
1. If anyone works out the truth, both Melisa and Kufa will get killed.
2. Kufa's still a lying, dead-eyed bastard who's keeping a ton of secrets from Melisa, starting with his true profession. He wants to keep her alive, but if necessary he also wants to be the one who kills her. Being an assassin isn't even his darkest secret. He can and will mind-wipe people who find out the worse one.
3. This is a post-apocalypse world of lycanthropes, vampires, magical libraries, genetically inherited character classes and aristocrats who'd have a thirteen-year-old assassinated. Everything looks civilised, but that's because we're in the world's last city-state, which exists under glass. There's a lot of weirdness in the background here.
Alas, all this would have had more tension if I hadn't known it was a light novel adaptation. We know it's an open-ended story that's basically going to maintain a status quo. Furthermore, Kufa is in many ways a classic light novel protagonist. He's mild-mannered and polite, but secretly has god-level fighting abilities that destroy combat suspense. Girls are attracted to him, but he refuses all temptation.
The good news, though, is that this is Melida's story, not Kufa's. She's the one who'll get real drama to face. She gets more action scenes than Kufa and she's outclassed in almost all of them. Ep.2 grabbed me, for instance, with its toxic "friends" and Melida's refusal to back down from her no-win battle and its life-or-death stakes. She can switch from depression to fierce aggression if you flip the right switch.
I like the show's sincerity. Our heroes are in danger throughout, since the baddies are probably right about Melida. There's real drama in the relationships, e.g. ep.5 undercutting everything that fights normally try to be, or the shocking decisions of ep.9. Rewatching the show in the light of what we learn there would be a very different experience. (Ep.6 is obviously a leg-pull, though.)
STUFF THAT'S MORE QUESTIONABLE
Ep.8 is a little over-compressed. Were they trying to adapt a bit more material than would comfortably fit into one episode? It feels as if we're missing some connecting material and logical links. (There's a cameo git who makes some unsupported assumptions of guilt, for instance.)
Why no apostrophe in the title?
What's going on with those cat's eye bodices?
Ep.6 has magnetism that makes you fly, albeit in an unimportant scene. I wouldn't have minded if they'd just said "magic", but they don't. And yes, it's "magnetism" in the original Japanese dialogue, not just in the subtitles.
I'd been a bit nervous of this show after hearing a one-line synopsis, but I enjoyed it. I like the romance, the drama and the dark premise. I'd like to get a second series, if only to dig deeper into the weirder bits of worldbuilding that we still haven't properly unexplored. Melida's lovely and I like Kufa too. I'd recommend it.