Naver Webtoon / Imperfect Sisters

I've only read the beginning so I can't really gush about it yet, but the green-eyed one is the older sister and the pink-eyed one is the younger. They aren't biological sisters; the younger one was adopted. It feels like the younger one was brought in to suffer in place of the older sister when she was sick. As they grow, the green-eyed one gets less sick and the pink-eyed one gets sicker, and the sicker she gets, the more obsessed she becomes with her sister, which is a delicious dynamic. So far, the parents of the green-eyed one seem like the worst.