Re: ADDITIONAL SPOILERS LIKELY IN THIS THREAD
Guy's probably done more towards shaping Luke than anybody else, and you can tell, because he just knows how Luke works, how to talk to him so he'll understand, how to (usually) calm him down... it's basically just adorable. And in my headcanon there's a part of Guy that's almost relieved when he finds out about the whole replica thing, because it's like Luke never really belonged to the Fabres, you know? He's an outsider, just like Guy is. Hee.