Board Thread:General Discussion/@comment-26544002-20151229000250/@comment-25942629-20151229012245

Apparently, Tenri Hiragi artificially inseminates a demon-possessed woman with his sperm. Shinoa and Mahiru were the only successes of that experiment, but they were considered normal children. The experiment was discontinued, and the two sisters kept their demons secret. Whether the demons are the ones who possessed her mother or spawned spontaneously as another part of their psyches is unclear.