After following the beginning walkthroughs, befriend Eric then get caught spying on him & Ann at night (after nude punishment starts).
That way you can fight his influence best. Also don't start any quests with sisters until you get rid of him. Don't do the Kira quest where he blackmailes you either! (unless you're into that). Doing the Eric as friend path watching him & Ann helps a lot also.
By doing the above first, you can explore all the content options with sisters from after he's gone. Saves loads of time playing each from beginning. He's a real jerk but it's very satisfying to beat him like this. Once you start private punishment with Ann, he's easy to beat. Enjoy!