Spectacularly messed-up... in theory. In practice, the anime backpedals on its premise and ends up replacing the manga's ending with a nice, fluffy anime-original episode that doesn't kill the hero. I can live with it, though. I enjoyed the show.
Firstly, the premise. Witches exist and they will grant your wishes. Great! Anything you ask for! They'll do it, but after that you'll only have two days to live. Your witch is also your executioner. It would seem that this is the witches' full-time occupation, tempting mortals into letting themselves be murdered. (Life energy appears to be part of the power that drives magic, so you could perhaps argue that technically they're vampires.) This is anime and so all the witches we see here appear to be young girls, but they're also all hundreds of years old and so any one witch's victim count hardly bears imagining.
They don't even question it. To them, it's just their job. When Rurumo (witch) appears to be getting too close to Shibaki (human client), another witch reminds her that it's unwise to get too attached to these people. That sounds like good advice to me.
Meanwhile our hero, Shibaki, is a massive and offensive pervert. His antics are intolerable. He's an open drooling libido with no self-control, the enemy of humanity and barely compatible with civilisation. Girls seem to regard his full name as "Shibaki the Pervert". I hated him. If you don't like bland, generic, personality-free heroes, have I got a doozy for you. He's a member of his school's Mysterious Discovery Club, who haven't realised that they're brilliant at sniffing out magical items that will kill you... and that's how he gets his hands on a grimoire to summon Rurumo. Things then get complicated, but by the time the dust settles, we have:
(a) Rurumo demoted to "trainee" for failing to kill Shibaki properly
(b) Shibaki in possession of 666 magical tickets that let Rurumo use her magic, but will also eat away his life. When he uses the last ticket, he'll die.
Rurumo herself is awesome. She's a stoic girl with almost no discernable emotion and no idea of how the human world works. (This must be the first time she's ever been near the same mortal for longer than 48 hours.) She's clumsy. She can get lost walking down a straight road. She understands nothing, but she tries very hard at things anyway. She also can't use her magic unless Shibaki burns away some of his life, which makes her powerless under most day-to-day circumstances. Her only friend is a talking magical cat (Chiro) and, bizarrely, Shibaki.
This is where things get complicated, by the way. It's as if there are two Shibakis. The normal Shibaki is a lech who needs kicking. However when Rurumo's around, he turns into her big brother. He barely even seems aware that she's a girl, although there are hints in the final episode that there might be something romantic going on. Shibaki's the kind of boy who'll take in stray kittens (ep.6) and there's clearly something like that going on with him and Rurumo, even though she's going to kill him.
Like I said, messed up.
Shibaki does indeed die in the manga, by the way, but there's a sequel manga series in which Rurumo does something about that and then a third series that's still ongoing. The ending's been changed for the anime, but I think that's forgivable since the manga continued with sequels and the anime is unlikely to. (Mind you, note that final shot of "4" on a clock. One of the Japanese pronunciations of "4" is the same as "death".)
So what's it actually like to watch? Answer: it's fun. The darkness pretty much disappears almost immediately. It's a light-hearted comedy with two dysfunctional idiots who could barely exist in human civilisation if it weren't for each other. They're funny and, despite everything, charming. Shibaki keeps going to endless trouble to protect and be nice to Rurumo, whereas you'd think the rational action would be to try to kill her.
Their adventures are standard anime hijinks, but with more porn mags. They have friends at school. They have comedy exploits. Rurumo studies cosplay, bras and swimsuits. Shibaki wages daily war with the school's Disciplinary Committtee, three girls who rightly regard him as the enemy. Also, every so often, the Mysterious Discovery Club will go looking for the Glasses of Unhappiness (which will kill you), a Swimsuit of Boldness (which rewrites your personality) or Werewolf Water (guess).
It's a fun show. Shibaki doesn't make it an easy watch sometimes, mind you. He really is a twat. However he's also Rurumo's best friend and guardian. Weird. Rurumo is always great, though, whether she's rewriting reality or demonstrating her lack of directional awareness, common sense or general knowledge. Chiro's a laugh, too. I hope they make a second season, preferably adapting the sequel manga, Makai-hen. Or I could just buy the manga and read it. Hmmmm...