Shoujo Gensou Necrophilia

Shoujo Gensou Necrophilia (少女幻葬ネクロフィリア, lit. "Necrophila of Darkside Sister") is a manga series by Akira Kazumiya. It was serialized in Comic Valkyrie.

Plot
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.