Squee! I love this pairing, and it's way too rare, especially with Lucius being pure bastard and poor Percy being utterly out of his depth.
I adored the way Lucius is obsessed with his feud with Arthur, and how he uses Percy as a weapon/tool to get back at his enemy. Nicely in character and vindictive :).
I mildly stumbled over a few overdescriptive adjectives (like red-headed, wealthy or older), but loved the characterisation, and especially the way you used the Imperius here - Percy being forced to to enjoy his own rape. That's deliciously twisted :).
My favourite part was probably the ending - plotting!mastermind!Lucius is one of my huge kinks, and this last scene keyed the fic so perfectly into the events in canon. Very, very nice!