This is an easy one, combine a whole clip of violence, a whole bucket of gore and a background plot of young assassins in love. It's no suprise at all that the distributor must have thought they had a winner here.
This could be difficult, as the opening intro pretty much does sum up this rather simplistic plot. Effectively we get to meet a young girl who was adopted by a rather seedy and suspicious cop after her parents were gunned down. He's molded her into an experienced and capable killer and also into his young lover. He gives her assignments, ostensibly of people who generally deserve it for some reasons, and she carries them out with unquestioning and brutal efficiency.
The situation becomes a bit more complex when she is required to hit two members of a three member group. It turns out that the third is the target of another assassin, a young male about her own age. And since they perform their hits at the same time they meet each other. This opportunity to share the knowledge of the rather specialized life they lead, something they clearly cannot do with normal friends, makes the situation more complex and somewhat `jolts' them out of the patterns they've been following. This also makes them consider what sort of future, and of what duration, there is for a young assassin. There's also the certain knowledge that those who trained them, are unlikely to offer much of a retirement package.
It's not a particularly long movie. It's also pretty obvious that they wanted a strong sense of style. The sort of cool atmosphere of dangerous violent people working in the shadow's of society. There's a lot of strange looking people, suggestive but minimal dialogue and actions as well as dark and gloomy meeting places. This sort of style makes sense for the contents being depicted, but it does mean that the depth of the story is both restricted in time and somewhat less important.
The characters are fairly strong, but not particularly introspective. While we get some quite graphic flashbacks to show how the female has become the killer she is (and she's pretty good at it) we don't really get to see any other aspects of her personality. The other characters, like the male assassin and the two controllers, get even less background. In a similar manner the actual reason for, and planning of, the actual hit is fairly minimal. It's fairly obvious that the story is secondary to the needs of the various scenes they wanted to have.
That said, as long as you are comfortable with this sort of thing, you might well enjoy it. While the characters are fairly archetypal they do have a sense of power and the dialogue, while minimal, fits the style fairly well. The action, barring a little bit of unrealism to make it more dramatic, is actually pretty cool. Complex moves, lots of incidental detail and buckets of blood. And given the cute toys these guys have, such as guns with exploding bullets and mini-grenades, the violence is graphic and large scale. It's a bit gratuitous, and probably not the sort of thing anime needs for its image, but it is not without a certain skill and power.
The animation itself is fairly good. It's bright, crisp and modern with some quite detailed scenes. The characters are quite complex but the action still moves cleanly and with some nice camera work. The only downside is it's a little bit cold and lifeless at times...so concerned with the `look' of a scene that it doesn't quite move as naturally as one would expect. Still, quite decent animation. The weapon design, and its effects, are well designed and quite detailed. The voices are okay, the dialog being quite laid back they're not called on to do too much, and there wasn't much music to be seen.
Apparently this has also been released in America in a director's cut version. The reason for the cuts was that the original included sexual domination as one of the ways in which her `boss' expressed his power and control over her. This may make the tape more intense, but it would definitely make it more hentai...and some may chose to stay with the edited version. I haven't seen it, but the Anime Critic has a review. Worth considering if you're looking to purchase a copy.