When I first started reading this I thought that it was actually decent. It seemed original, but I could relate Black Cat to this in many ways. I really enjoy the idea of assassins, and add fantasy and I'm sold. The art was good, better than a lot of other mangas that I have read. Main story isn't really there yet, but it's getting to it. All in all, it was good till...
It seemed like shounen-ai had thrown up all over this manga. I was fine with a little bit of shounen-ai like stuff, but that was... it was just weird and creepy.
Like what crazyboutcute had said, this is a very... sexual manga. In the action scenes, there is always some sort of sexual behavior that one opponent displays. Not only action scenes but the main character, Toneriko, always has someone doing something sexual to him, either speaking to him or teasing him, it's always something.
Originally, I would have given it an 8, but with the intense shounen-ai like aspects of this manga, and how there is just too much of an overboard of it, the rating I give it will be lower than it initialy was.
(Just as a side note, if the mangaka/publishing company say that it a shoujo, it is one.)