User blog comment:Crimson and Darkness/Shin DxD 3 discussion/@comment-2601:87:8300:20D0:3886:DF70:BE7:6028-20190823023509/@comment-10330822-20190823042904

I agree. Diehauser may not require AxA. Rather, I feel they are setting it up for Indra's team because AxA is the only thing we know that can allow Issei to fight multiple gods at the same time. Technically, Issei is capable of fighting two gods in the late game using a combination of DxD and Ddraig manifestation. This is how he beat Vidar and Typhon.

However, I don't think they need to pick between Fafnir and Ryuuteimaru. Part of my suspicion is that because Ddraig doesn't technically count as a familiar, he could possibly be used for AxA instead of Ryuuteimaru. Meaning Ryuuteimaru could be used for Asia's protection alone, however, part of me suspects if you aren't using Ryuuteimaru for AxA, you might as well just use Fafnir, because he is Satan-Class, and what's more, he can even fight someone of Crom's level for quite some time with Twilight Saint Affection constantly healing him.

Incidentally, Diehauser I feel might be beaten by the completed DxD G, because my suspicion is that Eros Engine will probably be his last upgrade, and Diehauser is his next fight. Since its short-term, what Ajuka said will probably happen and Ophis and Lilith have fused and temporarily combine to allow Issei free use of DxD G, as Ajuka said that is the short-cut for Issei to freely use DxD G.