SMT IV apocalypse - didn't actually finish, because finishing games are sad - is a story about your adventures as up-and-coming post-apocalyptic warlord trying to make it big in a post-apocalyptic world. It isn't so much a sequel as the previous SMT IV but an alternate retelling.
The MC is from the hunters association. They are more of a guild than a faction, and their members can be of different alignments. They assign various missions that you have do, eg kill / rescue / search for items. You start out as a gopher scavenging for loot and then end up dying on your first mission run, but you get resurrected by an old Celtic God called dagda (who probably came from the Norwegians). You then become the errands boy for dagda who slowly powers you up to become a god-slayer to take out gods backed by their own slayers. Depending on the choices, you can either side with the gods of existing status quo, the JudeoChristian Gods, or become the creator of your universe. They even have a throne chair for you. Which is totally badass for a 15 year old.
One of the best thing that they got rid of (not completely, but at least shoved to the side) was the the samurai/pan-European order of knights, which made no sense to me. These Japanese samurais wear these outfits that make them look more like knights templar, and they call themselves crusaders for kicks. I mean, seriously? You can only hide your international sales ambitions that much I guess.
They've got a plethora (yes, a plethora) of demons. Demon negotiation is back. Some of the dialogue made me pause for a bit. Like this demon turning me down because some pop group from the 2050s being outdated. Demons also have affinities on the scale of 0 (no affinity) to 7. So a demon with an affinity of 7 does more than 2x the damage of the a demon with an affinity of 3. Opponents also hit hard. I think one of the final bosses had piercing on light-dark skills that bypass your normal null/reflect/drain.
Overall a long game can go up at least to 100+ hours, but using citra/cheat engine you can probably do it in 60 or so.