Because no one is more badass than Hiei.
In my opinion the most badass scene from any anime character is the battle between Hiei and Bui in the Dark Tournament arc of Yu Yu Hakusho.
That fight was just the best and Hiei showed us for real that he is not someone you wanna mess with.
I thought it was great how he learnt to master the Jao Ensatsu Kokuryuha in a few days, especially after he busted his arm the first time he tried to use it.
The most badass moment in this battle was when he absorbs the Jao Ensatsu Kokuryuha when it turns on him. Screw trying to control the demon dragon, Hiei just loves to go the extra step and takes that vast about of demon energy into himself. Crazy fool, but you gotta love him for it.