Board Thread:Questions and Answers/@comment-25669979-20161220025242/@comment-25942629-20161231173633

Yes. Shinoa and Mahiru are half-sisters and share the same father. Some of the info on the Wiki is from fan translations, which have errors and need to be corrected later on. There were also many other half-siblings of theirs in this experiment, but they all died.

As I understand it, the mother was possessed by a demon. During pregnancy and after delivery, that same demon was passed onto the child from the mother.