Michonne's flaw is Delusions of BadAss-itude. Which is odd, because it implies she's not actually a badass. Except, loath as I am to admit it, she kinda is. So the end result is that she winds up with Delusions of Ninja BadAss Status, which is a prestige class within a prestige class that no PC characters are eligible for as of current rulings.

Symptoms include overly showy behavior, unnecessary scowling, excessive displays of pseudo-toughness, and severe katana abuse.