Chaosking
What I meant by others was that the plot seems to do everything in its power to set him up with overpowered heroines so I saw this as no different, or at least not much different.
Ancient_Egyptian:I don't know what you mean by others... but I can clarify what I meant. In short, everything goes according to the plan of the MC, maybe some cases progress too well, but the point still stands that it was under his lead... but here the opposite happens, he wanted to get rid of her, but instead, she suddenly becomes his sister? this is outside his plan and has nothing to do with his lead... even his mother's reaction is strange, he clearly states that he doesn't like her, and she love him so much to do something that could displease him deeply like this. So, this result either has a deeper meaning than just attaching new heroin to the MC or pure plot armour. And I am waiting for the coming chapter to know.
Man depending on what she did she may or may not be on my to kill wish list now. Depending on how this develops she might be as detestable as or even worse than Shira. Plus based on how far she went based on Xiao's character he would definitely decide to kill her so if you add her to the harem after that it would be too forced(and hateful).