As I said, I skipped over reading the NTR part and only read spoilers. So basically Choi starts breaking his mother, then his sister and his Childhood friend. This will go on for a while, his Mother breaks down the hardest.
His Mother doesn't just become a villain, she becomes THE villain, during the revenge part, she is the biggest threat.
She adopts a new identity as Min Sera and starts leading Choi's army as his second in command, Choi even falls completely in love with her and gives up everyone else for her.
What happens is that Childhood friend had been mostly broken but not 100%, and when she was torturing the MC, MC finally snaps and starts fixing himself. So she's the catalyst for that.
MC does fuck his mom too, he straight up makes his sister one of his harem members, though I don't remember incest babies between them.
Basically imagine that during revenge arc, MC is Batman who is kills and rapes, Choi is Joker and Mom is Harley Quinn, but she becomes more important and stronger than even Choi. MC does fix everyone.