User blog comment:Crimson and Darkness/Shin DxD 3 discussion/@comment-2601:87:8300:20D0:4578:499D:F51A:F5E6-20190801024042/@comment-2601:87:8300:20D0:40F:AC97:3640:C209-20190803020735

You're probably right but as far as we know there is no proof or mention that a king cannot be reincarnated because there is no King piece inside of them. I can imagine Roygun's wish would be to patticipate in RG, and say they only if under Issei and a lower rank.