Same Doge, she actually cares the power to fuck fate side-ways, wtf is her existence. Why doesn't she reincarnate both of them in a world where there is only them though? Even more so if he doesn't carry any memories
Of course she isn't going to be gone that easily, how else is this manga going to progress since it's built on the premise of a yandere sister doting on her older brother to such an extreme. I say this not as an insult btw, I'm actually disappointed that she isn't going to be off the story, but alas it has to happen..