>>283013988
Asa and Yoru being the same person and Asa becoming irredemably evil after spending 110+ chapters being a goody two shoes IS a twist. Also, that ignores Yoru's own development.
>hasn't the entire story been building to this moment?
No, that's just taking a stray line and justifying anything off it.
In the context of the phrase, "to live selfishly" for Asa was stop obsessing over her own mistakes, making friends and getting a boyfriend and Yoru already tried to use that rhetoric on her to make Asa become an evil psycho and it didn't work.