Heh, I thought I'd revive this topic. Now that everyone who is up to date with the manga knows about Kurogane's past, we can speculate about Fai a bit more.
I was thinking about a whole lot of stuff lately. Like, who gave Fai his tatoo? Why does he have it? Why did he create Chii? And does Fei wong Reed have a hand in this?
I clicked it all together a bit, and came up with one theory.
Fai had a sister. A sister who would've/could've been Freya or Elda. However, she got killed. (Fei wong Reed perhaps?) Fai snapped and his magic shot out of control. Lots of stuff was destroyed/killed. He could've subconciously created Chii to replace his sister. Kinda like with Minoru and Yuzuki from Chobits. Ashura, however, was able to stop major carnage by giving Fai that tattoo, to control the magic. (As Yuuko said, his magic does not come from his tattoo, but Fai swore not to use magic without it.)
However, one thing still doesn't quite fit. If Fai swore not to use magic without his tattoo, then who sealed Ashura? Surely, that would need magic too. Did Ashura seal himself, perhaps? I doubt it. If Ashura did seal himself, Fai wouldn't be so worried about him waking up and coming after him.
Did Fai perhaps make a deal with someone (Again, I refer to Fei wong Reed) to put Ashura to sleep, so he could flee?
Well, that's pretty much all I got right now. This time, a theory that has nothing whatsoever to do with a feather, or Ashura being a crazy dictator.