The Demon king has been mentioned many times over and over again.
"Successor of the Demon king"
"Nine members of the Demon Clan, namely the Ten Commandments known to be a group of elite warriors handpicked by the Demon King himself" Wiki
It seems that that there is still a ton of 7DS content to be shown. The demon clan battled against the Goddess clan and It was a close fight. It looks like we have not seen all the formidable opponents yet.
"Successor of the Demon king"
"Nine members of the Demon Clan, namely the Ten Commandments known to be a group of elite warriors handpicked by the Demon King himself" Wiki
It seems that that there is still a ton of 7DS content to be shown. The demon clan battled against the Goddess clan and It was a close fight. It looks like we have not seen all the formidable opponents yet.