Whoa whoa whoa, pump the brakes.
Don't you dare try to flip this around 72 chapters in. "She's been tormenting him all this time and became an idol to try and get his attention" is just about the dumbest fucking idea I've ever heard.
So... the way it seems to be going now from the little hint we got it will turn out that she's a childhood friend of his and as we all know childhood friends never win therefore i believe that there is will be a second girl with whom he will end up with.
people when a manga character is clearly portrayed as a sadist: i'm cool with it + my pp is getting hard
people when a manga character doesn't have the sadist tag on their face so they can see it: WTF IS THIS WHAT A FUCKIN BITCH HOLY SHIT!!1!!
plot twist: she probably got by mc back in Osaka when they were kids and she's ACTUALLY a masochist and all she's doing so far is so he can start bullying her again