The Cathedral of Shadows, also known as the Jakyou Manor or Heretic Mansion (邪教の館, Jakyō no Yakata)? in most translations, also known as the World of Shadows (邪教の世界, Jakyō no Sekai)?, is the location (or in some cases, computer application) where fusion of demons takes place in the core Shin Megami Tensei games.
The Cathedral usually contains several kinds of odd devices that are supervised by Mido, a head priest in blue. He offers services of fusing the comrade demons of a Devil Buster with no charge (except in IMAGINE). Several factors can affect the outcome of fusion, such as the phases of the moon (or Kagutsuchi), the status of the Devil Buster, as well as the demons currently under his control.
The demons fused in the Cathedral of Shadows are bound by an unwritten law of subjugation, where the newly formed demon will only serve under a master of equal or greater strength. It's for this reason that the head priest will decline fusing demons if the result is beyond the current capabilities of the Devil Buster. This limitation is often removed during New Game Plus.
- Megami Tensei
- Megami Tensei II
- Shin Megami Tensei
- Shin Megami Tensei II
- Shin Megami Tensei III: Nocturne
- Shin Megami Tensei IMAGINE
- Shin Megami Tensei: Strange Journey
- Shin Megami Tensei IV
- Shin Megami Tensei IV Apocalypse
- Shin Megami Tensei V: As World of Shadows
- Majin Tensei
- Majin Tensei II: Spiral Nemesis: As REMIX Station
- Devil Survivor / Overclocked
Unlike later games, the Cathedral is headed by a green, humanoid demon with a snake wrapped around him. He is replaced with the traditional minister in Kyuyaku Megami Tensei.
Shin Megami Tensei
The subjugation law is given an exception when the protagonist fuses his dog with another demon to create Cerberus, a demon whose level is well beyond the protagonist's own. This is because Pascal would retain his memories from the fusion and would still be loyal to his master.
Later on, the Chaos Hero will use the facility to fuse himself with one of the protagonist's demons to become a pseudo-fiend and increase his power tenfold. His purpose for doing this irreversible act is to merely exact revenge on Ozawa.
The Cathedral of Shadows was originally the place where a war criminal who was resurrected after being executed taught his disciples the heretical ritual used for his revival, and so it came to be known as the Mansion of Heresy. 
Shin Megami Tensei III: Nocturne
The Cathedral of Shadows can first be accessed in the Vortex World upon reaching Shibuya. Spirits there mention a cathedral with odd ceremonies being held every so often. The minister offers his services to the Demi-fiend, well aware of the incredible destiny the latter is meant for. The aforementioned services range from normally fusing demons to performing sacrificial fusion rituals at Full Kagutsuchi, demon enhancement by using Elementals and Mitama, as well as the Demonic Compendium where recorded demons can be re-summoned for a fee proportionate to how much it has been trained and strengthened by experience in battle.
The minister offers a special reward to the Demi-Fiend if he manages to collect all of the 24 Magatama - the Lord's Sword, Taira no Masakado's very own blade, capable of opening the way to the Bandou Shrine and to the ultimate Magatama, Masakados. He will also grant a 50% summoning discount if the Demonic Compendium is completely filled with the record of every obtainable demon in existence.
Shin Megami Tensei IMAGINE
The fusion mechanics in IMAGINE are basically the same as their core series counterparts, with the exception of the compendium, and triple fusion.
Triple fusions in IMAGINE require the participation of three different players, each of which must offer a different demon. Only the player starting the triple fusion will receive the resulting demon. When demons are at friendships of Open Hearts or Linked, it's possible for participants in the triple fusion to receive their crystal during the process.
There is no compendium for summoning departed demons in IMAGINE, only one for keeping records of their information. Acquiring the records of many demons grants various bonuses such as the ability to fuse certain unique demons and for every demon summoned to gain stat bonuses. Demons can be stored at terminals in most cities, but once they are used in fusion, they can not be regained unless they are refused or recruited again.
Additionally, the success rate of a fusion depends on the relationship level the player has with their demons. The higher the relationship, the more likely a fusion is to succeed. Should a fusion fail, the demons will be returned, but the player will still be charged the fee for the failed attempt.
The Ikebukuro cathedral also introduces new fusion mechanics, such as the ability to achieve 100% success in double-fusion and the ability to perform triple-fusion solo. These require payment in the Ikebukuro currency Kreuz and much higher demon friendship requirements than normal.
Shin Megami Tensei IV
The Cathedral of Shadows is added to a Samurai's Gauntlet once they have spent the APP Points necessary for it. It is run by Mido. The App is stored on a server which the gauntlets access to use the app. Fusing demons now rewards experience to the summoner and their demon when it is used and comes with a detailed search function that looks for demon fusion formulas. The Cathedral can now summon demons directly from the compendium for fusion if the summoner has the macca for it.
Shin Megami Tensei IV Apocalypse
The fusion system in Devil Survivor is a program in a summoner's COMP. In the fusing program, called "cath.exe", there are two modes, Fusion and Search. In Fusion, the player can fuse two demons they own together to make a whole new demon, on the condition that the resulting demon's level mustn't be higher than the protagonist's. In Search, they can search for demon combinations they can perform, and research categories such as race, existence (Confirmed or Unconfirmed) and previously owned by the player's party.
- In Nocturne, the player can listen to the classic Jakyou Manor BGMs from prior Shin Megami Tensei games by having a Cerberus or an Orthrus demon in the party when entering the Cathedral Of Shadows during a New Kagutsuchi phase.
- This is also the music played in IMAGINE's Cathedral.
|Playable||Akemi Nakajima - Yumiko Shirasagi - Cerberus|
|Non-playable||Minotaur - Medusa - Rick - Loki - Gaia - Hecate - Izanami - Seth - Lucifer|
|Daimakyuu||Micon - Tower of Daedalus - Bien - Valhalla Corridor - Mazurka Corridor - Rotting Sea of Flames - Infini Palace - Hades|
|Terminology||Demon - Hinokagutsuchi - Magnetite - Moon Phase System - Cathedral of Shadows (Fusion) - Rag's Jewelry - Izanami Clothes|
|Lists||Demons - Items - Spells (Kyūyaku)|
|Games||Megami Tensei (Telenet) - Kyūyaku Megami Tensei|
|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|
|Characters||Protagonist - Azura - DB Mikanagi - DB Kano - DB Kuroe - DB Yamaguchi - Kuzaka The Wise - Lord Judah - Madam Justice - Lord Doukan - Ogami - Setsu - Snakeman - Yamamoto the Steel-Willed - Louis Cyphre|
|Locations||Arcadia - Cathedral of Shadows - Ichigaya - Ikebukuro - Nakano - Protopia - Second Home - Shibuya - Shinagawa - Shinjuku - Shinjuku Babel - Souhonzan - Suginami - Third Home - Ueno|
|Dungeons||Suginami Tunnels - Basilica|
|Music||"Amatsuchi" - "Haru Megido"|
|Terminology||Cult of Gaia - Demon Buster - Great Cataclysm - Innocent - Millennium Kingdom - Obelisk - Order of Messiah - Seven Philosophers - Yagi - Chain of Curse|
|Archives||Demons - Skills (Features)|
|Characters||Protagonist - Gore - Jimenez - Zelenin - Arthur - Alex - George - Captain Jack (& Jack's Squad) - Ryan - Bugaboo - Mastema - Anthony - Dent - Norris - Kato - Williams - Muccino - Irving - Chen - Terry - MacCleary - Mia - Gekko - Blair - Zoe - Maebe - Wolf - Tyler - Mackie - Mike - Dawson - Keema - McClane - Louisa Ferre - The Three Wise Men - Mem Aleph|
|Locations||Red Sprite - Sector Antlia - Sector Bootes - Sector Carina - Sector Delphinus - Sector Eridanus - Sector Fornax - Jack's Squad HQ - Sector Grus - Sector Horologium - Womb of Grief - Empyrean Ascent|
|Terminology||Schwarzwelt - Demonica - Demon Summoning Program - Delphinus Parasite - Magnetite - Macca - Moon Phase System - Cosmic Egg|
|Lists||Demons - Bosses - Skills - Forma - Equipment - Items - Apps - Extra Missions|
|Music||Shin Megami Tensei: Strange Journey Original Soundtrack|
|Other||Aogami - Sophia|
Tao Isonokami - Yuzuru Atsuta - Ichiro Dazai - Miyazu Atsuta - Hayao Koshimizu - Sahori Itsukishima - Shohei Yakumo - Nuwa - Gustave
Abdiel - Khonsu - Vasuki - Zeus - Odin
|Tokyo||Jouin Academy - Shinagawa Station - Takanawa Tunnel|
|Da'at||Expanse: Shiba - Hamamatsuchou - Tokyo Tower|
Tree of Knowledge
|Terminology||Nahobino - World of Shadows - Bethel|
|Mechanics||Demon - Turn Press - Moon Phase System - Alignment - Fusion - Race and species - Difficulty|
Skill Potential - Magatsuhi Skills - Essence - Glory - Miracles
Cadaver's Hollow - Miman - Treasure Boxes - Amalgams - Demon Statues - Abscesses
|Lists||Bosses - Skills - Items (Vending machines) - Status Changes - Side Quests - Demons|
|Promotion||Daily Demon - News|
|Other||Demon Colosseum - Merchandise|
|Overclocked - Manga|
|Playable Characters||Protagonist - Atsuro Kihara - Yuzu Tanikawa - Naoya - Amane Kuzuryu - Keisuke Takagi - Midori Komaki - Mari Mochizuki - Kaido - Black Frost - Gin - Misaki Izuna|
|Non-Playable Characters||Haru - Shomonkai Founder - Gigolo - Yasuyuki Honda - Shoji - Azuma - Commander Fushimi - Beldr - Jezebel - Belzaboul - Belberith - Metatron - Okuninushi|
|Locations||Shibuya - Aoyama - Roppongi - Ikebukuro - Akasaka Tunnel - Omotesando - Shinjuku - Akihabara - Nagata-Cho - Shiba Park - Ueno - Kudanshita - Asakusa - Kanda|
|Music||Devil Survivor OST Remix - Reset - Soul Survive|
|Terminology||Extra Turn Battle - COMPs - Shomonkai - Tokyo Lockdown - Demon Summoning Program - Laplace Mail - Death Clock - King of Bel - Devil Auction - Dance Skills - Skill Crack - Racial Skill - Auto Skill - Demon World - Four Devas|
|Archives||Demons (DeSu - DSO) - Skills (DeSu - DSO) - Status Ailments - Titles - Endings|