In game you have a compass with a "north". How does the vortex world have a "north"?
In our world, North and South correspond (roughly) to the Earth's magnetic poles. While the Vortex World may be inside-out, it could also have some sort of geological feature by which navigation is made easier. In all likelihood, however, it wouldn't be the same as the cardinal directions we know now and the characters knowing how to navigate would be a case of Informed Ability or Gameplay and Story Segregation.
Even the souls in the game acknowledge "south" and "north" are mere relative terms in the Vortex World.
Also, the world may be turned inside-out, but it follows the basic map of Tokyo from the outside world even if not totally faithfully, a map that did had a north. The vortex world may not have a north, but the people that know where the north was before then can guide themselves through that.
So... if YHVH is the definitive "God" of the SMT verse, what the hell is Kagutsuchi?
Also God. YHVH and Kagutsuchi are two aspects of the "Great Will", YHVH being the authoritive persona, and Kagutsuchi being the creative power.
Why does the bottom level of hell look like a theatre ?
Because imagination is of the devil.
So, Hijiri is stuck in a loop of death and rebirth, right? So why isn't he seen after Isamu kills him again?
He is stuck in a loop, yes, but part of the curse is that he is doomed to be reborn on other worlds, meaning that he has to witness the desctruction of multiple worlds without being able to do anything about it.
He also spends some time between being reborn having his soul tortured in hell according to backstory. Then he gets reborn. Also he survived the first time because he wasn't aware of the situation and would have just died with everyone else unknowing as to what was going on. Part of his curse is that he has to realize just what's going on and how one can change things (ie create a reason) but then be denied the chance to do so. When Isamu kills him he's now perfectly aware of just how badly he failed, so he was free to pass on, get tortured and then be reborn to again to realize how the cycle works but have his chance to do anything about it snatched away.
If you use Lilith in battle, she will say something during her spells that is unclear to this Troper. I'm curious about what she says.
Shin Megami Tensei is full of nonsense words. Go and ask someone who's good at understanding their lyrics.
Why is Matador considered so hard? I agree that he can easily beat you the first time you battle him, but so will every boss in this game and any RPG player worth his salt will devise a strategy to easily beat him by spamming agility depleting attacks ans using a wind nulling magatama and wind resistant demons. So why does he have this reputation?
For starters, he has a move called Red Capote which makes his agility/accuracy skyrocket, he can use Dekunda to nullify any buffs you put on him (such as Sukunda). And when he Turns Red, he'll use Taunt to drastically lower your defense before following up with Andalucia — a multi-hit attack that hits like a truck at that point in the game. Like you said, you can make it a lot easier by equipping a Null Force Magatama and recruiting some demons who are Null/Resistant to Force, but it's essentially a beginner's trap. Oh and you can't attempt to run away and prepare yourself, unlike the majority of the other Fiend battles.
Matador, being a boss added to Nocturne Maniacs, breaks the difficulty curve a bit. He's the only boss in that section of the game that doesn't have a weakness, and he has a gimmick that makes him nearly impossible to hit. New players, and players who don't understand the value of status buffs and debuffs probably won't recognize the options available to counter his strategy. More experienced players will see right through him and have an easier time.
Is the Minister at the Cathedral of Shadows a human?
If he's anything like his previous incarnations (especially the very first one), maybe? If he's like the one in Digital Devil Story, he would be human but a human from Makai if that makes sense.
This is a minor one, but why is Loki holding a 1000 Yen Bill in his room? The world has come to an end and the new world's currency is Macca, so a 1000 Yen Bill is essentially worthless except as something to collect, but you really get the impression that no one in the Vortex World shares the Collector Manikin's fascination with humans. Why would Loki keep something with absolutely no value?
Well, in Shin Megami Tensei, there's a guy who will buy "old world" money for Macca. So I'd say collector's value.
Did buildings just spring up overnight in the new world or did somebody actually build them? Because you lived through the end of the world and woke up in one that had structures in it that were definitely not present in the old one. You'd think there wouldn't be enough time to build all those buildings in the apparently short time you were asleep.
The Vortex World is created before your eyes at the beginning of the game, but the inhabitants post-Conception act like it's been around for a long time.
So what happened to the rest of the world during the Conception? Were they destroyed, or turned into other Vortex Worlds?
As far as can be told, it's all gone and the pieces of Tokyo is all that's left. They definitely aren't other worlds, it's made pretty clear that it's one universe for one conception.
It's been awhile since I've played, but I'm pretty sure an NPC says that our world split into several vortex worlds, which in turn will be reborn as new universes.
During the Amala Labyrinth quest, after you reach the Hell Maze you find out that one of the Manikins managed to escape into the Vortex world with the Afterlife Bell. When you go to the cemetery to get it from him you find his remains. According to a nearby spirit he died because he returned as a human and humans can't survive in the Vortex world. If that's true then how are Chiaki, Isamu, Hikawa, and Yuko able to survive?
All those characters survived through the Apocalypse as humans. That random Manikin turned himself back into a human.
During the creation of the Vortex World, what happened to Earth as a planet as well as the cosmos it inhabits? Did the entire reality collapse into a Cosmic Egg, or would someone up on ISS suddenly see Earth turn inside out and become a tiny, sealed sphere traveling through space?
The way it's explained in-game, it's the former. The entire reality is gone with the Vortex World as its remains, and through the World's power, it awaits for resurrection or destruction.
Isn't it awfully strange that Dante and Raidou if you hire them are perfectly ok with destroying the chance to rebuild the world forever and then pick a fight with god? Or for that matter just leave the world a desolate hellhole if you get the regular demon ending. I mean they probably didn't want to add a mechanic for them to turn on you if you pick an option they disapprove of, but it seems like they signed on with the idea that you'd be fighting Lucifer (to kill him I mean. Not the testing your strength battle you get in the end) and wanted the original world restored.
It could be that they did turn on him behind the scenes, once they realized what he intended to do, and tried to fight him. But considering that at this point the Demi-Fiend eclipses them many times over in sheer power, they were probably Killed Offscreen for getting in his way.
Or maybe, to provide a less grim interpretation, they decided that Lucifer and the Demi-Fiend, however manipulative and destructive they respectively are, are at least a better option than the Great Will, leading to an Enemy Mine situation.
How did Hijiri find out about the Conception?
Probably a similar way to how Hikawa found out - ancient cryptic texts, sources in various apocalyptic cults and secret societies, and perhaps a certain amount of premonition/instinct given that he's been through this shit an untold number of times.
What is Lucifer's plan if you die during your battle with him in TDE? Kagutsuchi is gone, not just for this world but for ALL worlds - which are implied to be utterly destroyed as well. Which means that you're the last human in existence - the last possible candidate to be his right hand in the upcoming battle. What's his fallback plan if you die?