Necrophile of Darkside Sister

[MrTerrorist]

From Mangaupdates:
Georg and Riselotte are your typical brother and sister, except the former’s a priest and the latter’s “alive” by way of…darker methods. As a result, Rise is stuck in a child-like body. Georg immerses himself in research to free Rise from these chains.

Spoiler for ch1-3:

If you finally figure out the title then yes, Riselotte is a zombie. The story goes like this, Georg makes a deal with a demon to resurrect his dead sister Riselotte in exchange for Riselotte eats human flesh for him in order to keep her body "fresh". Georg knows he can't keep his sister alive like this forever so he's also searching for the Necronomicon to free Riselotte from the demon's spell and return her body to normal. However, he has to avoid the Inquisition who are on a hunt for those who deal with the Dark Arts which his childhood friend Silvia having becoming one of them and a mysterious Doctor and his sister.

Be warn! While the manga has cute lolitas, there nothing cute a dead girl who is forced to survive by eating dead corpses. Plus the story can be depressing as well.

[MrTerrorist]

It's been a long time.

Spoiler for ch4-8:

So Doctor Crowley and his sister Claudia also have a demon like Georg and Rise except this demon can turn into a human girl. Crowley suspects Georg is looking for the Necronomicon which he is also looking as well. To confirm his suspicious, he manipulates Georg's fellow priest whose a grave robber, Silvia, the Inquisition and the priest who took care of Georg and Rise and Georg himself by telling them what to do or making them tell him either by subtly or force.

Now, Crowley knows Georg is after the Necronomicon, Georg is looking for the book itself which unknown to him, is stolen by Crowley's demon and Rise and Silvia realize "the disease" that's affecting Rise might not be normal and they know Georg isn't being honest with them.