The world of DDS is a sequel of sorts to Shin Megami Tensei III: NocturneHitoshura/The Demi-Fiend sided with Yosuga, and produced a world where the strong devour the weak. This explains the cannibalism, the presence of the Demi-Fiend, and, to an extension, why the goal of the game is to euthanise Brahma, who is this world's manifestation of the Great Will, the end of the second game was a more positive "Conception."
The world of DDS is another world within the Amala NetworkFor starters, The Lady In Black did mention that the Earth that Hitoshura was born in, was one of many in the Amala network. The spinning barrels atop of the heads of Brahma's many forms are Amala Drums, but are used for a different purpose within the DDS world. God's power could be explained as him using Brahma as another avatar of his because: the way that the world was deleted is like what happened in Nocturne, but much stronger and God works in mysterious ways in BOTH series. Plus the Hitoshura as a Bonus Boss could be interpreted as Lucifer trying to recruit more demons in a different world, asking his most trusted General to go scout the worlds.
The Demi-Fiend is so powerful that you only won because he wasn't going anywhere close to all-outThe Demi-Fiend is definitely one of the toughest, if not THE toughest, of bosses in a series already known for being Nintendo Hard. Yet if you've played Shin Megami Tensei III: Nocturne, where he was the protagonist, the attacks he uses here (the Mute-causing Javelin Rain, Heat Wave, Stun-inflicting Xeros-Beat, and the overkilling Gaea Rage) were attacks that were fairly mediocre, as well as the demons he calls. The only demon that could probably do well in Nocturne's endgame is Titania (though the Megidolaon-casting Pixie is certainly nothing to sneeze at). Yet Gaea Rage does SEVERAL THOUSAND damage when your HP cap is 999, and that assumes your stats are near their max. Now imagine he was actually TRYING. Enter Metatron, Shiva, Beelzebub, Red Rider, Daishoujou and DANTE. Meanwhile he'd be throwing Focus'd Spiral Vipers and Freikugels all over the place. Not to mention he'd be using the Masakodos magatama which nulls EVERYTHING EXCEPT ALMIGHTY.
The Tribhvana are the humans that Jinana, Mick and Bat were based off of. Especially with the latter, because there is that one member who (like Bat) is utterly batshit insane.
The Four Angels and Meganada were members of the World Stabilisation Committee that tested the Demon Virus on themselves
Greg's Junkyard Avatar (Lupa) was deliberately introduced into the simulation.