Megami Tensei Multiverse

The Megami Tensei Multiverse collectively refers to the many worlds and universes included in the Megami Tensei series. Nearly all Megami Tensei games mention hints of connections between different dimensions or planes of existence, as well as collections of universes which all suggest the games may not occur in the same "universe" but that they still take place in the same over-arching multiverse.
==Theories==
===Digital Devil Story: Warrior of the Demon City===
Charles Feed theorized that each great, powerful demon was surrounded by their own "universe" and that only the one could be contacted at once. Thus, upon Loki's death, his universe collapsed and Set's universe took its place, which is why Ohara accidentally contacts Set with the Demon Summoning Program.
===Shin Megami Tensei III: Nocturne===
The Lady in Black explains to the Demi-fiend that his world is just one of many and that the Conception was simply the destruction of the old world, which didn't affect the multitude of other universes in the vastness of Amala. Kagutsuchi rises, matures and falls in billions of places, other universes which will experience their own Conception and creation of a Vortex World for the sake of rebirth, all in accordance to the Great Will's cosmic intentions. By siding with a Reason, the Demi-fiend is able to choose the rules of the new universe born in its place.
Demons and gods are capable of using the Amala to traverse across universes, with the "false gods" from Shadow Vortex in particular seeking Vortex Worlds in order to be reborn along with the universe and becomes real. The Lady in Black also mentions both she and her master, Lucifer, has spent aeons to travel across the Amala, having witnessed the birth and death of countless universes.
=== Raidou Kuzunoha vs. Soulless Army ===
The Akarana Corridor is a tunnel binding several timelines together as parallel universes. Humans and demons with the necessary means to travel this expanse can freely go back and forth between universes, however they must take care not to lose their origin points and become Lost Souls.
Raidou Kuzunoha XL left his timeline in order to seek a world in which he can create a new future, as he was unsatisfied with his own present. Rasputin was sent in order to apprehend him, but he chose to abandon his mission in favor of indulging his own desires. At one point, Raidou Kuzunoha XIV gets expelled from the universe and ends up falling into the parallel universe of Raido Kuzunoha XIV.
=== Raidou Kuzunoha vs. King Abaddon ===
Lucifer invites Raidou here for his final quest in New Game+, "In the Coast of Time...". This, combined with his own dialogues, heavily implies that he is a demon who came from another timeline seeking a "spark" which will finally create a world free from the control of God.
===Shin Megami Tensei IV===
In the incident 25 years before the events of the game, the world split into three parallel universes as a result of which path - Law, Chaos, or Neutral - Flynn's former life had chosen. Flynn himself is a result of the Neutral path, with a ceiling covering the entirety of Tokyo and its surface became the Eastern Kingdom of Mikado.
Chronologically, all three universes of Tokyo are occuring at the same timeframe, as the cataclysm which took place 25 years ago is frequently referred to by residences of all three universes. Through the Yamato Perpetual Reactor, it is possible for humans to traverse the Expanse into these parallel universes. Sufficiently powerful demons and entities such as the The White are also capable of naturally traversing it.
===Shin Megami Tensei IV: Apocalypse===
Stephen explains to Nanashi the universe he resides in, as well as others connected through the Expanse, is an extension of the Great Reason (Axiom in English), the collective origin as well as the grand manifestation of all things contained within itself. YHVH could once be considered an extension of its will, but he was forsaken at some point in the past due to not conforming to its intentions.
To counteract this, the Axiom brings forth Messiahs- special humans containing a portion of its power, acting as its means to observe and interact directly with lesser beings. In the case of Flynn and Nanashi, its intention is to break YHVH's hold over his home universe by any means necessary. 
The multitude of ways in which humans, demons and gods have interpreted the nature of the Axiom is due to the fact that it cannot be called sentient in ways lesser beings can understand. Only the most powerful of transcendent beings such as Stephen can come close to comprehending its nature, and even they struggle to do so.
Due to a lack of detailed information, it's currently unclear if the Great Reason and the Great Will mentioned in other universes are in fact two names for the same entity, or if they are different entities entirely.
The "Messiahs in the Diamond Realm" DLC point out there are differences in travelling across interconnected universes (such as the parallel universes of IV and Apocalypse, via the Expanse), and between universes with no inherent connection. In both IV and Apocalypse, humans and demons can independently move through the Expanse into various parallel universes. However, Stephen specifically mentions he needs to bend the Reason in the natural order of things (in English it is changed to "immutable rules") to allow Nanashi to meet with and extend a chance of salvation for the other Messiahs from different universes. 
This suggests the Megami Tensei Multiverse is divided into several "groups" of universes, each group consisting of a certain number of interlinked universes. While ones in the same group may naturally interact, distinct groups cannot interact under normal circumstances. Bypassing this seems to require interventions from entities on Stephen's level in order to twist the natural laws of reality, with the developers of Apocalypse stating only Stephen and entities like him such as Mido and Saint Germain being the same persons across the entire series.
== Universes/Dimensions ==
===Digital Devil Story: Megami Tensei===
* Assiah
* Atziluth
===Megami Tensei II===
* Earth
* Makai
===Shin Megami Tensei===
* Earth
*Makai
* Diamond Realm
* River Styx
===Shin Megami Tensei II===
* Earth
* Makai
* Diamond Realm
* River Styx
===Shin Megami Tensei: if...===
* Earth
* Makai
** Land of Nomos
* River Styx
===Shin Megami Tensei III: Nocturne===
* Earth
* Vortex World
* The various Worlds born of each Reason:
** Shijima
** Musubi
** Yosuga
* Labyrinth of Amala
* Shadow Vortex
===Shin Megami Tensei: Strange Journey===
* Earth
* Schwarzwelt
===Shin Megami Tensei IV===
* Earth
* Blasted Tokyo
* Infernal Tokyo
* Expanse
* River Styx
===Majin Tensei series===
* Earth
* Amnesia
* Paranoia
===Devil Summoner series===
* Earth
* River Styx
* Alien Dimension
* Extra Dungeon
* Paradigm X
* Corridor of Time
===Raidou Kuzunoha series===
* Earth
* Dark Realm
** Alternate Earth of Raido Kuzunoha the XIV
* Akarana Corridor
* Infinite Abyss
===Persona series===
* Earth
* Maki Sonomura's dimension
** Avidya World
* Female protagonist's reality
* Nether-realm
* Sea of Souls
* Midnight Channel
* Metaverse
** Palace
** Jail
* Theater District
** Hikari's Theater
===Devil Children Red/Black/White Book===
* Earth
* Makai
** Ice Expanse
** Wind Expanse
** Earth Expanse
** Forest Land
** Fire Expanse
** Center Expanse
* Deep Hole
* Tenkai / Sanctuary
** Grass Field
** Crystal Ring
** Cosmo City
===DemiKids===
* Earth
** Future Rem (Nature/Wasteland)
* Dem
** Fire Dem
** Ice Dem
** Center Dem
** Underworld Dem
** Sand Dem
** Future Dem (Dead Lucifer/Living Lucifer)
* Deep Hole
* Valhalla
===Devil Children Fire/Ice Book===
* Earth
** Future/Past Harajuku
* Makai
** Future/Past Makai
** Deep Hole
* Niflheim
** Future/Past Niflheim
* Muspelheim
** Future/Past Muspelheim
* Ginungagaap
* Tenkai
** Future/Past Tenkai
===Devil Children Messiah Riser===
* Valhalla
* Makai
** Fire Expanse
** Ice Expanse
** Wind Expanse
** Earth Expanse
** Center Expanse
===Digital Devil Saga series===
* Junkyard
* Earth
* The Sun
===Devil Survivor===
* Earth
* Heaven
* Demon World
===Devil Survivor 2===
* Earth
* Akasha Stratum
* Providence
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