Pupa is an manga about a brother and sister. They get a unknown disease the sister becomes an hungry human-eating monster but the brother reacts differently to the disease and becomes like an immortal. Also their Farther is abusive .
Yandere: Utsutsu Hasegawa (aka the brother I talk about earlier)
Yandere scale: 9.5/10
All this yandere wants to do if make sure his sister is happy and save and most importantly alive, even if it means she has to eat him. To him his sister is everything to him.
My opinion: I love this story, it hard to explain why it probably because I've never seen something like this before and I find the idea really cool. Also their is to many yandere senes to count!
Manga images: