I remember reading this particular manga more than 8 years ago. The only thing I'm sure of is that it's a dark story that is set in medieval Europe about a brother and his undead/zombie sister. The brother is a priest or someone who works in a morgue and he feeds his sister parts of the dead to keep her alive while keeping her existence a secret to the villagers. Other parts I'm not sure of is that their parents were a part of some cult that worshiped demons and the siblings were being abused and an ritual resulted in the death of the sister. Tried mangas with the zombie tag and unfortunately it's none of them. Even looked for it on mangaupdates and still couldn't find it.