Too blinded by love I think
Uh... Idk how you came to that conclusion since I'm kinda complaining how it doesn't make sense that she likes her sister that much in the first place. Is sisterly love at first sight a thing now? And strong enough to overshadow ANY kind of other emtions that should at least be brushed on? Sorry not sorry, but I don't see how mc can go to "nooo, I killed my family!" to "welp doesn't matter, have a new sister now lol" with a smile on her face.
That whole background story feels like it's whole purpose is just to have an excuse to have some kind of obstacle between her an ml ╮(─__─)╭
She is supposed to be an ordinary girl before being isekaied into the novel, right? A girl with a loving family. Which she felt died because of her. Not even a single tear just because she has her new twin sister in the novel? Huh??
Girl, even if it's your favorite novel... The disconnect between events and emotions in the MC is baffling.
Rebecca doesn't seem very likable to me either. Sure, influence of the demon king yada yada. The jealousy is real tho? She made a wish to the demon king. She wanted to be saintess so badly she was willing to sacrifice her family? Did I really get that right? And you still want to save her because of the 'guilt' from your previous life?
These are some really big events that should be impacting ones life drastically, instead they are just used as an elaborate setting for a romance with her favorite character, it seems orz