I'm still toying on easy mode, yet I can't manage to reduce Aria's willpower by 80 points without the serum that transforms her into semi vegetable state lol!
Any tips on this?
She's not really much harder than Rebecca (usually the first one I break in). Take her fighting with you to raise her respect to at least 20-25. Upgrade the bedroom, living room, and bathroom for the passive persuasion and arousal bonuses. Compliment her if you want to (it'll fail frequently unless you have really high charm). Ask her to take a bath with you (at 20 respect she'll agree sometimes). Take one by yourself if you have to so you're clean.
Ask for sex (not seduction or bondage, just straight up ask for sex), start with blowjobs since they seem to have a better chance than vaginal or anal. Ask using the casual/charm option at first, not the demanding one unless you start with really high manipulate. She'll turn you down some of the time and agree other times and that will build happiness and affection with her. If you do the demanding option she'll lose affection for you every time she refuses you. If you do the casual/charm option she won't suffer any negative effects for refusing you.
Once you get her happiness up around 80 or so and her affection up to at least amiable then you can try seduction if you want. Prior to that seduction is a waste of time on her unless you have stupidly high levels of charm. Same with bondage except there it's manipulate that's important.
Once you get her to loving or better affection she'll agree to let you tie her up and have some fun with her in the dungeon. If you want that to be guaranteed, put her in one of the 2 main slots and turn on morning blowjobs for her. She'll definitely refuse at first and gain some defiance which will give you an excuse to take her down to the dungeon. But even with that option you want her to have a reasonable amount of affection for you or she'll start with negative arousal which will make the session almost a guaranteed failure.
I haven't picked her up in awhile so I can't remember for sure, but I think her intelligence is also low enough to qualify for the Daria's Gift bonus which gives you a 20 pt charm bonus with all the girls who have low to mid level intelligence.
Another option is starting with the teen subduer perk. She melts like butter if you take that, along with every other teen in the game, especially after you've gained a few points of charm.
Personally, I find seduction to be the most effective way to reduce willpower once you get her to the point where she'll agree to sadistic/dominant tactics. Start the seduction with the aggressive option, that has a chance to reduce willpower. So does using dominate/heavy petting during the foreplay. When you get to the sex part take the sadistic option, that reduces willpower the most. Then split your time between fucking her pussy and her ass and end by cumming in her mouth. Make her lick your balls afterwards, that also drops willpower. When you cum in her mouth, have her hold it first before swallowing, that gives an extra willpower reduction. Some of those options have willpower/affection thresholds where she won't do it until you reach those levels but you can drop her willpower by more than 5 per seduction session pretty reliably and by closer to 10 if you get a few lucky rolls. Always pick the most dominant/aggressive options once she likes you well enough to accept it.