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You can skip if you want to, because very major spoilers ahead
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From what I understood of the novel, MC isn't the OG Illyana. Like she has her body but the soul is different. They aren't even a reincarnated version of the OG villainess, just someone who got misplaced after the real Illyana got lost from dreamwalking so far away and couldn't find her way back to her body.
OG!Illyana isn't completely human, she's half demon as well from her father's side, hence the ability.
So really, she' suffering the consequences of what the real villainess did to the ML despite not being the one to have done it at all, and the reason she is letting him get away with 'taming' her and all the torture she's gonna go through is a mixture of fear and misplaced guilt (that if the body she is in didn't hurt him, he wouldn't turn out the way he did). Plus, she thought once he feels like he gets his revenge, he'll get tired of her as well.
i can’t get over how she’s not even the one who did all those things to him but has to suffer for it its so frustrating ( ̄へ ̄)