I'm going to expand this to manga since I don't watch that much anime.
Negi Springfield from Mahou Sensei Negima! Smart, on-the-fly strategist with more magical firepower than the dominant empire on Mundus Magica...at the price of his soul? Unlikely, given that it's a shounen manga, but it could happen yet.
That's without mentioning the bevy of females that willingly follow him around and help him out, all of whom are nothing to sneeze at, both physically and magically.[footnote]By the way, if you haven't yet, you should really read this manga. It starts picking up around volume 7 and never slows down. I have yet to be disappointed with it. In fact, it well may be my favorite manga ever. xD[/footnote]
Alternatively, I'd be Yoh Asakura from Shaman King. He has got to be the most laid-back guy I've ever read about.
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