User blog comment:B214/Volume 21 info & spoilers/@comment-26926813-20160313124909

And finally:

Issei and Vali vs Aposhis and Azi-Dahaka. I am waiting this since summer 2015. Diabolus Dragon and EJOD.

Also I think that DxD mode of Issei is stronger than EJOD because Rizevim's SGC cannot reflec the damage from Issei form, but EJOD dont work on Rizevim if mention Vali's commentares in Volume 16.