So... for the fun of it, I've been working a slight bit on a Darksiders/Shin Megami Tensei crossover. It mainly a work in progress, but I've got some things I felt like sharing. Mainly on how I am going to try incorporating the lore of both series together.
FIRST, the Horsemen! Considering both Darksiders and SMT have their own Horsemen of the Apocalypse, and this is a crossover, I figured we could cut the latter series'... sorta! The Four Horsemen from Darksiders (Nephilim Horsemen) will exist as the primary looks essentially, while the Four Horsemen from SMT (Fiend Horsemen) will be basically a form that some will see them in, primarily "lesser" demons that could be easily taken out by them, such as Slime, Preta, and Onmoraki.
Considering how some other series have characters who's form shifts depending on the one viewing them, I believe the trope is called "A Form You Are Comfortable With", I can kinda see SMT playing with it. Actually, if I remember correctly, Lucifer's demon form is sorta like that in SMT V/Vengeance, isn't it? We only see his true form in the end in part because he wishes us to see it. Everybody else that seens Lucifer sees his demon form when he shows up to them as far as we can tell.
So here, instead of the Fiend Horsemen, maybe the Demi-Fiend ran into other Fiends during his journey. I'm thinking David, Chemtrail, Plasma, and maybe En no Ozuno or Alice. I think David could be funny to see, I just kinda grabbed Chemtrail and Plasma because they are Fiends, and I think En no Ozuno could be interesting to see make a bit of a comeback in SMT. All in order, the Fiends that Naoki will defeat and then take command of are Matador, Daisoujou, Hell Biker, Chemtrail, Plasma, David, Mother Harlot, Trumpeter and likely Alice. I am so on the fence with En no Ozuno, I'm still doing research on the character and from what I can find, he's one of the more powerful Fiends, so an idea popped in my head of him and Demi-Fiend being about equal in power and so neither is able to command the other. Maybe the same could go for the Sage of Time... Huh, a neat idea of there being three Fiends at the top who are about equal in power and can command the less powerful ones... Yeah! I think I'll go with that!
This does give me the idea that Naoki, En no Ozuno, and Sage of Time can all summon the other Fiends, though will usually split the overall number when all three higher level Fiends are going about things around the same time. Something like Naoki gets Matador, Daisoujou, & Hell Biker as En no Ozuno takes Mother Harlot, David, and Trumpeter while Sage of Time has Chemtrail, Plasma, and Alice. Or maybe En no Ozuno has Chemtrail, Plasma, and Trumpeter while Sage of Time has David, Alice, and Mother Harlot. I think Demi-Fiend primarily having Matador, Daisoujou and Hell Biker makes sense in some ways, so he would keep them while the other two major Fiends will get the any of the other less powerful Fiends.
Then there's Aogami & Kei, the Nahobino. I did once have the idea of them being the same Creator that is mentioned in the Darksiders games, but I feel like going with them becoming the next Creator as they do in their home game. As I type this out, I had the idea of them meeting Ulthane. Maybe not in combat but maybe as like a side quest giver, sorta similar to some of those side quests where you can give a demon in the overworld an item for something in return. Something like that Jack Frost you can give Ice Gems, just something else with Ulthane, though I am unsure what at this moment.
...That is all I got for now! Hoping to come back to this post soon and add more to it later. Hope you all enjoyed!