User blog comment:Ariel Saeba/Mythology and Character Origins in DxD/@comment-27876048-20160510232127/@comment-24.113.252.213-20160511022044

The fourth Horseman seems to have something to do with the "wild beasts of the earth," and Hades was mentioned. The only Sacred Gear user who I believe fits this description is...

Leonardo from the Hero Faction of the Khaos Brigade.

Reasons:

1. He has the Sacred Gear Annihilation Maker. Granted, the beasts he creates and controls aren't "of the earth," he still uses beasts.

2. He is currently in the Realm of the Dead, where he and George are studying magic under a famous dead magic user. Perhaps Hades will make an appearance with Leonardo in tow and he'll use his beasts to fight.

At least this is what I think. I welcome anyone to build on this or introduce a new theory. I really enjoy discussions like these.