User blog comment:B214/Volume 22 spoilers/@comment-187.195.211.194-20160726161803/@comment-180.183.121.8-20160726173553

Issei will remain being pawn of Rias even if he started his own peerage. An only way to get new pawns for Rias is trading Issei with other King since she already used up all 8 pawns.