The Diamond Realm (金剛神界, Kongō-shin-kai) is a location within the Expanse in the series.
Shin Megami Tensei
Just before the ICBM launched from the U.S. nearly hits Tokyo after Thor's defeat, the Heroine teleports the protagonist to the Diamond Realm to ensure him unscathed in the missile attack. The protagonist is woken up by En no Ozuno, who offers him tasks to gain enough strength before returning to the devastated world. First, the player searches the area to retrieve his lost demons and regroup with Law Hero and Chaos Hero, who are also transferred here, then En no Ozuno asks them to obtain a Soma from the pond somewhere at the outer rim of the realm. This task is performed twice - the first time En no Ozuno consumes the Soma instantly, the second time he tells the player to keep it for themselves.
Afterwards, En no Ozuno asks Law Hero and Chaos Hero to leave the protagonist's party temporarily and requires him to obtain two powerful melee weapons in the middle ring area of the realm. Each weapon is possessed by a powerful Phantom, which will hand over the weapon if it shares the same alignment with the protagonist, otherwise battle ensues. After this second labor, En no Ozuno allows all three heroes to leave the realm, but they are blocked at the exit of the Diamond Realm by Zenki and Goki as the final trial to prove their strength to survive the barren land.
The player can visit his servants, Zenki and Goki, next to his room. Zenki saves the player's game progress while Goki heals the party for free.
Shin Megami Tensei II
The Diamond Realm is an optional dungeon but requires a separate file of the player when in the underworld. Once the player defeats YHVH and finishes the game, the player must then load up the 2nd file and speak to a specific NPC in the 2D Underworld Map to access the Diamond Realm. It is here the player can fight and encounter Fiends. There are also separate gates that have specific stat requirements to open.
Shin Megami Tensei IV: Apocalypse
The Diamond Realm is a location that is only accessed in the DLC quest "Messiahs in the Diamond Realm". Stephen requests Nanashi's assistance via a Challenge Quest. After accepting the quest and arriving in the Diamond Realm, Nanashi is greeted by En no Ozuno. Zenki can be spoken to via the door to the right of En no Ozuno if Nanashi wishes to leave, and Goki, through the door on the left of En no Ozuno, can provide healing.
After exiting En no Ozuno's room, Stephen explains to Nanashi that four other messiahs, each from their own respective universes, were feared by and thus ended by YHVH. Stephen, in retaliation, had interfered by bending the laws of the universe and salvaging the souls of the four other messiahs. Stephen shows Nanashi the salvaged soul of the Hero, whose cycle of reincarnation was ended by YHVH, and explains that the other three messiahs are similarly left incorporeal and fighting throughout the Diamond Realm. Stephen says that he is not permitted to guide their souls back to their respective universes, but explains that Nanashi can, as Nanashi's power can return the Hero's soul to its original form. He requests Nanashi be a guiding light for the Hero, and is willing to extend his salvation to the messiahs even at the risk of bending the will of the Axiom. Later, prior to fighting Stephen, Stephen will reiterate that this power of Nanashi's is that of observation, which can be inferred Stephen no longer has as a result of him transcending his own humanity. Stephen will also later explain that Nanashi's potential, humans' power to change the world and exceed the Axiom, is necessary, as well.
From there, Nanashi will go "greet the other messiahs", as Stephen puts it. The encounters can be done in any order, with Aleph and the Law Horde located in the Northwestern section, Demi-fiend and the Chaos Horde located in the Northeastern, and Flynn and the Neutral Horde located in the Western. The Aleph and Demi-fiend encounters will provide Nanashi with the Blue and Red keys, respectively. The Flynn encounter does not provide a key, but is still necessary in order to progress. After completing all three encounters and returning to En no Ozuno's room, En no Ozuno will take the Red and Blue keys to open the door located in the Eastern section, explaining that Stephen and the remaining soul await them there.
Stephen's room is denoted as having an evil presence. Inside, Stephen requests Nanashi's power for the Hero's soul. Stephen will link the two messiahs to each other, an experience that leaves Nanashi dizzy. Stephen explains that Nanashi's sensations will be fed back into the Hero's soul, and that with their souls linked, the Hero will be able to observe Nanashi. Nanashi must then battle Stephen until the Hero regains his original form and remembers who he is and his goal. Afterwards, the Hero thanks Nanashi for aiding him.
However, despite restoring the Hero, Stephen isn't satisfied. Demi-fiend, Aleph, and Flynn barge into the room and Stephen gets up from his chair. Stephen states that the reason he was willing to extent his salvation to them is because he believed in their human potential, and insists that they show their potential to him in order to prove that he made the right decision in bending the immutable will of the Axiom for them.
Prior to the battle, the mere presence of Stephen's power is overwhelming. It is enough to explicitly affect the messiahs, with the exception of Demi-fiend and the Hero. Nanashi, who is noted for his fearlessness, feels a knot in his chest; Flynn, who typically steels himself in the face of battle, appears visibly distressed; Aleph grunts and remarks on Stephen's imposing presence and tells the others to be on their guard.
The Hero will note that Magnetite is flowing out of Stephen before the battle starts.
Shin Megami Tensei
|10||Azumi||Brute||Neutral-Chaos||51||Rf: Elec||1||Zio - Media - Water Wall||Sanjiegun|
|15||Kimnari||Yoma||Neutral-Law||62||Wk: Ice / Ab: Fire||1||Agilao - Bufula - Hapirma||Pearl|
|15||Gandharva||Fairy||Neutral-Neutral||75||Rs: Expel||1||Zio - Lullaby - Happy Step||Bead|
|15||Nue||Wilder||Dark-Neutral||88||Wk: Gun & Fire||1||Feral Claw - Stun Bite - Panic Voice||Turquoise|
|16||Tan-Ki||Beast||Neutral-Neutral||140||Wk: Gun & Fire||1||Sukukaja - Squash - Water Wall||Bead|
|16||Tsuchigumo||Jirae||Neutral-Law||80||Wk: Force, Magic & Alm||2||Shibaboo - Hama - Toxic Sting||Poison Arrow|
|19||Bugaboo||Jirae||Neutral-Law||105||Wk: Force, Magic & Alm||0~1||Bufula - Mabufu - Rakukaja||Mabufu Stone|
|19||Nekomata||Beast||Neutral-Neutral||106||Rs: Expel||1~3||Zanma - Marin Karin - Feral Claw||Bead|
|21||Apsaras||Yoma||Neutral-Law||152||Rf: Elec||1||Rakukaja - Makajama - Media||Tomoe Sword|
|32||Blue Phantom||Meta||Neutral-Chaos||310||Rs: all||1||Agilao - Maragi - Shibaboo||Soma|
|32||Red Phantom||Meta||Neutral-Law||320||Rs: all||1||Zanma - Mazan - Diarama||Soma|
|Zionga - Rakukaja - Might
Makajama - Tarukaja - Media
|Goki Claw (Visionary)|
- Boss name is highlighted in red background.
Shin Megami Tensei IV: Apocalypse
|Playable Characters||Protagonist - Heroine - Law Hero - Chaos Hero - Pascal|
|Non-Playable Characters||Stephen - Ozawa - Yuriko - Old Man - Gotou - Ambassador Thorman - En no Ozuno - Louis Cyphre - Soul Diver|
|Locations||Tokyo - Kichijoji - Shinjuku - Ichigaya - Diamond Realm - Shibuya - Roppongi - Ginza Underpass - Ginza - Tokyo Tower - Shinagawa - Ikebukuro - Ueno - Tokyo Destinyland - Basilica - River Styx|
|Terminology||Terminal - Alignment - Ring of Gaea - Order of Messiah - Great Cataclysm - Sword fusion - Four Heavenly Kings|
|Soundtracks||Shin Megami Tensei Sound Collection|
|Archives||Demons - Bosses - Skills - Items|
|Playable Characters||Aleph/Hawk - Hiroko - Beth - Cerberus - Lucifer - Satan|
|Non-Playable Characters||Okamoto - Gimmel - Zayin - Stephen - Haneda - Daleth - Red Bear - Madam - Hanada - The Center's Bishop - The Four Elders - Mekata - Puck - Hanoun - Mutant Elder - Hiruko - Taira no Masakado - Siren - Petersen - Michael - Raphael - Uriel - Gabriel - Fake YHVH - Seth - Virocana - Ozawa - Gotou - Gemori - Astaroth (Ishtar / Ashtar) - Kuzuryu - YHVH|
|Locations||Tokyo Millennium - Underworld - Expanse - Eden - Diamond Realm - River Styx|
|Terminology||Millennium Kingdom - Great Cataclysm - Order of Messiah - Ring of Gaea - Terminal - Sword fusion - Identification Program - Summon Doll - Seven Pillars of Solomon - Sabbath - Abaddon's Innards - Megiddo Arc|
|Content||Demons - Bosses - Skills - Items|