Saw a lot of talk about Jin, and I'd like to throw out a suggestion.
Instead of trying to"purify" Jin, what about trying to make her less submissive? A few days after buying her, Lin has an event where she wants you to start showing her sister what her new life is like. So you start taking her out, letting her choose where to eat, what to wear, etc. Basically easing her into freedom. Gives her a chance to subtly come into being one of the interactable harem rather than just springing it out of nowhere.
I also like the drug thing, but that would be workable with this scenario. Jin has been a slave for so long, she had to cope somehow. But when she found she didn't
need the drugs anymore, she got sloppy. Maybe even did it intentionally in her subconscious as a cry for help, but either way Lin catches her and goes totally nanners. That would lead right into your story, and as someone else said, would let us help her through her issues like we've helped all the other girls through theirs.
Just an idea I had, feel free to use it to bounce off of.
Whatever you decide for it, I'm sure it'll be amazing.