User blog comment:B214/Talk About What You Want! 3/@comment-101.175.92.231-20150218091212/@comment-1359322-20150218222818

The reason why i can say it decisively is because of these two statements.

"Full members! Just like in real chess, you can have a maximum number of 15 servant Devils under your control.

It seems like High-class Devils receives 15 [Evil Pieces] from Maou. You can form a master and servant relationship by using it to those who you want to make as your servant."

- Volume 2

"Those that were reincarnated like me as well, a lot of them were through the activity of the rating game valued and were let into the group of upper class devils, and stood on the same level as their master. And it seems that, from the Maou-sama they receive their Evil Pieces to use for their servants. At that time, they become Kings.

Well, there is a rule where they have to come participate as the piece of the Master in battle who they’re at the same level as. In devils, for the master, the fact that they are their families devil never changes. For instance, let’s assume I become a 'King' in the future, for Buchou’s game I shall still be a 'Pawn'."

- Volume 4

So the [King] is only a position a Devil gain once they get their 15 Evil Pieces.