HMMM....

Who knows at this point she’s an enigma

I'm confused... Where in that whole ball scene did you get the notion that the sister is obsessed/a masochist for the MC? I'm genuinely curious.
Have you ever read any manga/manhwa like this one before? Cause stuff like that happens all the time in them.
From what I understand, Alexa's sister did all of that to try and destroy Alexa's public image so that she can't climb the social ladder and compromise her position. She goes after Alexa's fiancee so that when he chooses her over alexa, (the old Alexa who was in love with him) Alexa would make a scene about it but ends up embarrassing only herself. Of course that didn't happen because she isn't the org. Alexa.

Idk if it's just me but none of her sisters actions scream that shes obsessed with Alexa....

Ye I agree with you. But maybe on some alternate universe the sister is a yandere and only wants the sister for herself??? Like she wants to cut everyone away from her and only have Alexa rely on her?? I have no idea

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someone say her sister actually care about her

Ooh.. yes yes, this is what I'm thinking that's why I got into the conclusion of the MC sister is kinda obsessed with her.

I've read some Manhwas that about like this too but the sister acts really different especially in the hunt comp. But just like Yup said and that's what I'm also thinking that's why I think she's obesessed with our MC