User blog comment:B214/Volume 23 discussion blog/@comment-2804:D41:4A9B:E500:1D4F:A397:BB70:B3C2-20170726041337/@comment-10330822-20170728083757

I agree, Bennia. It also makes more sense why all four of the Satans were involved, if it was just about testing Issei's capabilities as a Gremory Sirzechs would better suited to do that by himself.

Despite forfeiting his title of heir to become a Satan, Sirzechs still seems to be the major power behind Gremory. I'm sure he still works with his father, but we saw during Riser-Rias engagement party that Sirzechs isn't above taking actions of the house without his father's say. He approved Issei's duel agreement that Riser would duel Issei for Rias's hand, even though that isn't necessarily his call to make. Despite being the leader of the Underworld, Sirzechs shouldn't have that kind of authority to jeopardize an engagement like that.

Also, as you pointed out, Sirzechs and the other four Satans testing if Issei is worthy of Rias's hand is also odd, that's something that you'd think her parents would have to do. Sirzechs probably used his influence to take control of the ritual himself to accomplish additional plans.

To take it further, Sirzechs beat Issei down despite Issei already proving his power is other fights, to properly test his limits, and Ajuka took the chance to expand Issei's abilities further, allowing Sirzechs and Ajuka to further possible plans for Issei by taking his current limits into account.

My guess is that Sirzechs took a liking to Issei after he dueled Riser for Rias's hand, obviously because Rias means so much to him already, and eventually he sold Ajuka on possibly using Issei has their poster child.

If you think, a lot of the stuff that has gotten Issei in the public eye is probably Sirzechs and Ajuka's doing. The approval of his duel with Riser, his service as a bodyguard during the Three Factions peace summit, his participation in the Young Devil Gathering, his training under Tannin, Issei being assigned as Odin's guide and fighting Loki, maybe even Issei's meddling with the Human Faction's plans in Kyoto. Definitely his addition to the DxD is their doing. They all could have been planned by Sirzechs and Ajuka to push Issei further and faster into development. Likewise, like Oppai Dragon show increases Issei's popularity to the point that his reputation precedes him almost everywhere now. Not to mention he now has his own financial security from the show.

Everything that happens with the Three Factions in the human world seems to happen in Issei's figurative backyard or his literal home. Basically forcing Issei to be in the center of any ensuing chaos.

Chances are even the stuff that seems like Zeoticus's ideas are actually done on Sirzechs's advice.

This ExE group is probably just another step. Making Issei the poster child for security, peace, and power in the Underworld, undermining blood supremacists and other rebellous factions. While at the same time giving Issei more and more leadership experience to take the "trump card" role he has among the Alliance by the EX series in the far future.

Personally, it would surprise me if Issei is head of the Underworld and Alliance military by the EX period, and the ExE group is just a special force group composed of Issei's children and his closest allies.