User blog comment:B214/Volume 23 discussion blog/@comment-31137559-20170209174955/@comment-5480911-20170213230338

Season 4 would be a good point to end the anime, especially since if they adapt volume 10 and we get that scene with rias and issei they would offically becomea couple.

it really is a miracle that dxd already got this much adapated already, most series especially harem focused series only ever get 1 to 2 cour adaptations and never more, the fact it got 3 seasons is already an amazement and 4 seasons an absolute miracle and if u add the 4 total plus the 4 ovas that is over 52 episodes total.

if s4 is the last one and they stick to the light novel story this time it will end well but i am hoping at the very least we get another season after to adapt the rest of the story arc that will start with s4 and s5 would be even a better option to end the anime adaptation there.

That is just my opinion.