User blog comment:B214/Volume 22 spoilers/@comment-27083298-20161112215056/@comment-26821288-20161114075725

Well, even if Issei will use DxD, Crom would still be a really tough opponent. So maybe Issei and Bina Lessthan will need to fight against him together. Unless Issei got a much better mastering of DxD than he had against in Vols 20-21. Although in Vol 21 he fought against Apophis and defeated him... which is an impressive feat, so he might actually have a chance against Crom.