I'd been vaguely wanting to watch this for twenty years. I saw a trailer for it and thought it was charming, but then never got around to buying the DVDs and simply forgot about it. At last, though, I've dug it up.
It's rubbish. It's also amiable and good-natured, but I pretty much hated it.
MANGA = I haven't read this, but I know it's very different. In its brief three volumes, a schoolgirl called Nana gets split into seven copies of herself. They all go to school together. It's also sexier than the anime.
ANIME = bloody hell, where do I begin? Nana gets split into seven, yes, but they decide that they mustn't tell anyone about this because you can't make 26 episodes of pointless idiocy if people start being sensible. They all want to go to school, for instance, but Keeping The Secret means they can't. Furthermore, Original-Nana wants to pass an exam, but the others generally slob around and don't bother studying with her, even though a seven-Nana study group would have been a powerful exam-passing weapon (especially since one of the Nanas is superintelligent) and in addition not studying means they'll be worse than useless if original-Nana gets sick and one of them has to take her place in school.
The Nanas also have superpowers. Eh? What? They can fly, lift impossible weights, etc. Despite the secret-keeping about there being seven Nanas, they don't see any need to avoid, say, flying around in superhero costumes and having conversations with people.
The Nanas all have different personalities. Original-Nana is bland and useless... no, wait, I'm not meant to say that. Let's say "shy and timid". The others give themselves nicknames. Nanappe is short-tempered, Nanakko is easy-going, Nanacchi is sunny, Nanarin is a crybaby, Nana-sama is brainy and Nanapon is the sexy one. (The Nanas are, though, only 14 years old, so we're talking about a bland, kiddie-friendly sort of sexy and the show's TV episodes couldn't be tamer. Theoretically, the OVA 26th episode has nudity, cleavage, etc. but the show's still basically for small children and you don't see anything there either.)
...in theory. In practice, there are only two kinds of Nana. Original-Nana fancies a boy she doesn't dare approach and wants to study for some exams but is bad at them. These two things are linked in an uninteresting way. Meanwhile, the freeloaders are a six-headed blob of irresponsibility who mostly just slob around and occasionally do some superheroics.
Some shows should theoretically be rubbish, but are rescued by their likeable cast, sparkling dialogue, etc. This is the opposite. I like the premise. The theme song is charming. Actually watching episodes, though, is a slog. The Nanas are little more than Brownian motion in a skirt, their actions never meeting their ostensible goals. Their schoolteachers are so cartoonish that having them on-screen is painful. Nana's crush, Yuuichi, is nice enough but again bland. There's no point in watching these people. I didn't care. (Nana's best friend Hitomi is cute, though.)
I like the few occasions when Nana manages to have a meaningful conversation with Yuuichi. The characters are undeniably nice, after all, and I was never in doubt that Nana's feelings were real. There's a significant revelation two-thirds of the way through. I still like the basic idea, but this show is dead-set against meaningful exploration of it. It's a bit tiresome. Nana pins her faith on good-luck charms, shows terrible future planning, suggests sleeping for 2 hours a night instead of 4 in order to fit in extra studying, tells obviously absurd lies to try to hide the existence of her copies, etc. Don't even consider watching this.