On top of things, they did a good job of showing he's really 17 and makes all the mistakes a 17-year old is expected to make. Anime heroes rarely act the age, unless they see women bathing or something. (I guess one of his refreshing points is also his sexuality, or lack thereof) I don't watch Busou Renkin, though I read the manga, and I have one thing to say about Kazuki : DORKY TEDDY BEAR. XD

One of Taniguchi's ideas about growing up/teenagers, exemplified in Ryvius, is that they're horribly selfish. This makes good story. It seems to be so in this case as well.