Since dlc characters get their "story" in DOA6, that would be a decent way of putting a VF character and Ein into the game. Story-wise I think that Hayate knows Karate and can use it at anytime if he wants to, so he doesn't have to re-learn it, just use it...for whatever reason. Still, if I'd have to choose between Kiryu and no Ein vs Ein and ANOTHER VF character, I think I'd go with the 1st option.