Asuna from Negima!

Negi Springfield
He's so hillarious and by far the most badass british 10-year-old ever =P

and his badassness increases as the manga goes on

as for favorite character... dmn, this is hard to pick... but... I think, out of all the characters he's ever done, I think I'm gonna have to choose Mai from Itsudatte My Santa. After all, a rather flat-chested brunette who can become a buxom blonde is simply ftw... Santa, like so many of Ken's male leads, is such a lucky bastard