Monster Children is the collective term used to describe the children bore by the Demon Lord and succubus Rapture. There are 16 in total, and they are all cursed with malignant urges to reproduce by their mother, whom they scorned by ruining her perfect appearance upon birth. They only reside in the "Fake Dimension".
They spawned a new species referred to as mamono, demons who are structured anatomically similar to humans and have the same mannerisms, although the curse still effects them.
They will play a major role in the upcoming J-Tournament arc.