Detective Grim Reaper

This is about a grim Reaper leaving the soul realm, coming to earth stopping the summoning of behemot. But the problem was he been dead for centuries meaning whoever have a piece of behemot body part is more likely to get summon which mean trouble. You see their was a bunch of crazy scientist doing a demon experiment which lead to a creation of regreta (re-gre-ta) and this person or thing have many different body parts form humans to angle to demon and one of then is behemoth tail. if this earth cult try to summon behemoth it won't summon him but it will summon regreta who is extremely high class dangerous the last time we try to capture her/him almost kill the devil king. so now it up to the grim Reaper to find a host and try to stop the summoning from happening........ if possible......... hopefully.