User blog comment:B214/Volume 22 spoilers/@comment-24173056-20160611141433/@comment-24.113.252.213-20160614034802

I know he'll remain an 8-piece Pawn in Rias' peerage. Since he already has Evil Pieces within him, he can't use a King Piece. But he can still become King by touching the monument in the Satans Territory.

Read the Evil Pieces page.