The premise is simple enough, one of six gods has been found to have violated some rules, he is stripped of his power and the rest are looking for a replacement, specifically, one of his children with mortal consorts who retain enough divinity...
There are a total of 8 contestants, one of which is the unclean beast, and that one makes no sense at all.
Most are simple enough to understand, the proginator knocked up a female of one race or another and a demigod was born. You got fairy, angel, vampire (specifically mentioning him being born to a vampire mother and that they have nursing customs so its not unusual)... the oak is an empty suit that USED to contain a knight, but the body decayed over countless years of getting mortal wounds until just the suit contained him, the rook was a castle built by a demigod, he fell in battle to defend it and demanded to be put in the highest chamber where he merged with the castle, and he can unmerge to become just the untouched body in that bedroom.
But the unclean beast happened when a "tome of darkness" had gotten one of al saleem's wives pregnant with a monster that literally chewed its way out of her. it said her life would be forfeit from the task, and the unclean beast is supposed to still serve the tome, it served al seyeed until he stopped obeying the indestructible book, and at that point the unclean beast ate him. So... any explanation?