I'm with Errant on this. Why isn't it any of the mental ability scores? Because the inspirational leader type should use his charisma, yes, but the wise or perceptive martial artist should use wisdom and the cunning warrior should use intelligence.
Also, what about these battle arts?
You gain Improved Unarmed Strike as a bonus feat, and monk unarmed strike damage as a monk of your class level. You add any Monk levels and Unarmed Swordsage levels you have to determine your effective monk level.
Martial Artist, Greater
You gain a +1 bonus to attack and damage rolls with unarmed strikes for every four Battle Scion levels you have. In addition, your unarmed strikes are treated as magic for overcoming DR.