User blog comment:B214/Volume 23 discussion blog/@comment-172.58.16.1-20170324223136/@comment-87.9.174.130-20170325002435

More than merging, he could do something like what he did with the Triaina and the Cardinal Crimson Promotion (true Queen). He could make another Illegal Move, a King promotion. Obviously it would be absolutely dangerous, so first he probably should need to train his body to sustain that power up and stabilize the powers of Ophis and Great Red he already possess to avoid the greatest danger (death). By the way, the King Piece raise your power, but if we think about it, according to power it could also refer to Demonic Power and Issei, without the Boost, never had great demonic power, he wasn't good at it. If that were the case, Issei could increase his control over his demonic technique beyond any imagination, like a gigantic dress break that could cover a whole nation. lol