Fuma is the loving brother of Kotori, and he takes very good care of her. He has a reputation at school of being very stern, but all the girls adore his strong silent nature.
Of course, in the ever-mangled anime, you don't see much of this. His descent into madness isn't nearly as reasoned (how many people just go insane because their sister was kidnapped? Especially when you remember all Fuma's been through as it is...) and it has none of the psychological nuances he inflicts on poor Kamui. You see none of the caring parts of the Manga. While the anime does have its merits, it can hardly compare to the manga.
I think my favourite bit of manga 1: Prelude, is the bit where Fuma kicks the ball through the soccer net. It's not so much the event itself, or even the reaction of the goalkeeper ('I thought I was gonna die!'), more the fact that's he's done it before!
Which X Japan song reminds me of Fuma? Well, it has to be 'I'll Kill You'. Check it out on the lyrics page and see quite WHY it makes me think of him...