Many do have that quality. It simultaneously bothers me and doesn't bother me. Meaning I'm a bit conflicted on it. I remember one my friend started watching (I forget the name of it), there is was basically the middle ages but there were also some witches involving themselves in human matters; my friend was interested because it was a relatively faithful representation of Medieval armor and weapons, which is one of his interests, if it's relatively historical. But the witches in that show were very sexualized as well, wearing little and doing the typical "Japanese girls do this" thing of feeling each others' breasts as a joke and the like.
I have read that the "ideal" Japanese woman is expected to be (or at least act) in a kind of demure and innocent way (even in bed). And that by having women who are comfortable with their sexuality and don't mind showing it, it's an assertion of confidence and self-esteem. Note that I cannot confirm the second claim at all, and I've encountered enough evidence for the first that I think it's at least an aspect of their society, if not a big one.
The anime is Dance in the Vampire Bund. I have no idea what it is at all.
Since it's dealing with fictional characters, I don't particularly care one way or the other. I imagine for most people it's either satirizing it, or they're just trying to avoid trouble (I know of one case in the UK where a man was arrested for artwork depicting CP - no actual living humans were harmed, but he was sent to prison anyway), so I just don't make a fuss either way.
I see what you mean though. I don't think anyone actually thinks it's not taboo, except that, by the letter of most written laws, it would be legal, so it can probably either be seen as a satire on the taboo nature of it or just a quick "run-around" of the law (I put that in quotes because it's not a particularly useful or effective defense).