An immortal being of both angelic and demonic heritage. Often mistrusted, and feared, by both sides for what they are. These beings came into existence when the first incubus, seduced and impregnated an angel. Thus, the first Niju (Plural: Nijusei) was born.
This caused the angels to hunt him, and the subsequent spawn, down. Not to mention, purify any and all possibility of such an occurrence from happening again. (Thus, without genders, Angels were further armed against the wiles of demons, where sexual temptation was concerned.)
They always havetraits of both their angelic and demonic ancestry, though usually one side is stronger than the other, sometimes so much that it's almost impossible to notice that you aren't speaking to a true angel or demon.
Their strengths and weaknesses mirror their appearance: A mixture of both angelic and demonic traits.