User blog comment:B214/Volume 23 discussion blog/@comment-172.58.16.1-20170324223136/@comment-10330822-20170325001128

Yeah, as Pawn said, Issei can't use a King Piece anyway, even if they weren't banned, because you can't mix something like his Mutated Pawn Pieces with a King Piece.

Although, I still feel that Issei may evolve "out" of his Pawn Pieces. Evil Pieces can't work on God-level beings, so it makes you wonder what happens when a Reincarnated Devil like Issei reaches God-level. If the pawn pieces deactivate and fall out of him or something, then he could take a King Piece.