Yugi: But, doesn't that mean that all other religions are wrong? And the hokey Ancient Egypt religion is the only real one?
Yugi: Huh. Didn't see THAT one coming.
Shadi: I did!
A fantasy setting with a premise that one particular mythology is an approximation of the truth, usually with some plot-relevant differences. This is often a mythology associated with a mainstream religion.
- In Attack on Titan, this turns out to be the case in-universe regarding both sides of the mythology regarding the Founding Titan Ymir. One side claims that she stumbled upon the very source of all organic material and became the first Titan in the world, and used her Titan to destroy the Marleyan people ruthlessly. Another side claims that she bestowed wealth upon humanity by paving the roads and building bridges through the power of her Titan. Both are correct, but neither of them was ever done entirely out of her free will. She did encounter whatever supernatural creature turned her into a Titan, but it was while she was running away from persecutors. She did build bridges, pave roads, and kill Marleyan people, but only because she was a mindless slave and did as her master told her to. And just like the legends say, Ymir died 13 years after becoming a Titan. Because she was slain, and then fed to her children.
- Though Boku Girl takes place in modern Japan and the only regular figure from Norse myth is Loki (plus her crow familiar), the whole pantheon is real and live in Asgard, even if they don't exactly fit the physical appearance (or even the genders) of the mythical figures.
- Uchibi Sasuke includes what seems to be traditional Asian mythology, as seen through the lens of the game Ōkami.
- Not Completely, Altogether Here: Elphaba's father and sister are devout in their faith in the Unnamed God. They both scorn Lurline worshippers as pagan heathens. As Elphaba learns after dying, Lurline is the god-like figure that heads Oz's afterlife. Upon learning this, Elphaba wishes she could see her sister's face. Nessarose has a hard time coming to terms with Lurline after she's killed. This is later subverted when an old man implied to be the Unnamed God appears.
- Expecting Someone Taller, by Tom Holt, to the Germanic pantheon.
- Good Omens, by Neil Gaiman and Terry Pratchett, does this with Christianity (mostly of a heavily Milton-influenced variety). Its Switching P.O.V. protagonists include an angel, a demon, and the Antichrist. Of course, part of the joke is that the popular culture version of Christianity is rather closer to the truth than what any organized Christian religion actually believes, and even then it's not perfect.
- J. R. R. Tolkien's early drafts of The Silmarillion, published in Lost Tales I&II, are a clever inversion of this: Through a series of events and battles that are echoed mainly in Norse and Finnish mythology Middle-Earth becomes our world. Tol Eressëa becomes England, Kortirion especially is identified as Warwick, and Elves still exist. The tales that Ælfwine/Eriol is told are the true pre-history of the world and would later be fictionalized among humans. This was toned down significantly to the point of near-abandonment in later drafts, though the fading of the Elves and the gradual dominion of humans remains a prevalent theme. Also impossible to get rid of completely: Some cunning linguists pointed out that a huge number of Tolkien's Eldarin word roots are built to act as predecessors of reconstructed Indo-European, theoretically transporting the idea of early humans using language they were taught by the Elves into the real world. See Faramir's quote on all speech of the world being Elvish in origin.
- The Space Trilogy by C. S. Lewis is a mixed example: it's explicitly Christian, but implies that Classical Mythology is based on the celestial politics of our solar system, with the planets' Oyéresu inspiring the gods.
- Roger Zelazny did this several times:
- Bring Me The Head Of Prince Charming (co-authored by Robert Sheckley), to Christianity — or its Theme Park Version. Mostly Played for Laughs.
- Creatures of Light and Darkness to Egyptian Mythology - in the far, far future.
- Eye Of Cat to Native American Mythology — in a far future, though nowhere near as far as the previous entry.
- Lord of Light pretends to do this, using Hindu Mythology, except that the Gods are actually humans with psychic powers and advanced technology.
- Implied though not outright stated in the Chronicles of Amber series. A close variation on Camelot is explicitly shown, and the various Princes are archetypal enough that one could fit them into various pantheons in Shadow with just a bit of a twist: Julian would be a hunter god, Benedict would be a war god, Oberon would be the ruler god, and so on.
- Welsh mythology in The Dark is Rising. More or less.
- Jonathan Strange & Mr. Norrell at the very least presents as true English legends concerning The Fair Folk, and Merlin is referenced as being a real person. At least, because in the story collection The Ladies of Grace Adieu and Other Stories, there is a Crossover with Stardust, and Neil Gaiman at least has placed Stardust within his All Myths Are True 'verse.
- In Douglas Adams' The Long Dark Tea-Time of the Soul, all the Norse gods and legends are true. Also involves a subversion of Gods Need Prayer Badly, as Thor comments at one point that humanity created the gods, but just because we no longer need them doesn't mean they go away.
- Tailchaser's Song has a domestic cat Creation Myth about how a feline God called Meercat Allmother created the universe for cats. There are also various Just So Stories about things like where humans came from (they're deformed cats cursed to act as servants for the superior cats for all eternity) and why dogs hate cats (a trickster cat once shamed a dog king). This all seems to be true because several of the legendary characters, such as the mystical Tangaloor Firefoot and his evil brother Grizraz Hearteater, are actual cats who the main characters meet.
- In The New Job, Ukrainian folk-Catholicism is pretty heavily implied to be true, considering the pious main character's occasional experience of visions and miracles.
- Ghost Roads: Rose's story neatly ties together some common variations of the hitchhiking ghost and phantom prom date Urban Legends, and provides an explanation for the borrowed coat that shows up in so many of them.
- The Shadowhunter Chronicles are Christian, or perhaps generally Abrahamic, as it throws in elements from Judaism and Islam too. (Cassandra Clare is Jewish, for the record.) Also a Fantasy Kitchen Sink, with things like vampires, werewolves and The Fair Folk incorporated in.
- Supernatural is an interesting case which can't decide whether it's this trope or All Myths Are True. Earlier seasons seem to imply the latter, with the characters explicitly stating that "almost all cultures" have lore of some kind about the Monster of the Week, with only slight variations. However, later seasons seem to run on the basis of Christianity (with God, angels, and Lucifer). A season 5 episode even addresses this issue with a gathering of gods from other/more ancient religions being mad that the Christian apocalypse is going to end the world instead of their own religion's version of the apocalypse. Lucifer promptly slaughters them, leaving Christian myth the only one relevant.
- Cleverman: Aboriginal mythology, called the Dreaming, turns out to be true. Waruu is versed in the Dreaming, enough that he recognizes important story related events around him.
- He identifies the creature that killed Uncle Jimmy by its work and its reason for showing up: "when things are out of balance".
- He also recognizes the story from Uncle Jimmy as an indication said uncle made his choice of who will succeed him as Cleverman.
- A story contained in Uncle Jimmy's journal tips Waruu off that sap from a particular tree can counter the Cleverman's Healing Factor.
- Chronicles of Darkness actually discusses this in "Inferno", a splatbook about demons. It's up to the Storyteller, in agreement with the players, which religion is true in regard to the myth of demons. This is a considerable improvement compared to Demon: The Fallen, in World of Darkness, which based its demons upon Christian teachings, but at the same time insisted that this was not the same Christianity as that of the real world.
- Scion normally assumes All Myths Are True; however, the campaign in Scion: Ragnarok assumes a setting in which only Norse Mythology is real. 2e's Companion gives advice on how to dial between one mythology being true and all myths being true for a setting.
- The first seven God of War games are in a setting based on Classical Mythology. Word of God said fairly early on that the world in total has a Crossover Cosmology, it just wasn't until God of War (PS4) introduced elements of Norse Mythology and Tyr's vault contained treasures gathered from many mythologies that we actually saw such.
- Touhou Project and Japanese Mythology. If you ignore the earlier games, anyway.
- Darksiders is this to The Bible and its Book of Revelation.
- BlazBlue is largely about Japanese Mythology. In particular, it's established that Amaterasu (aka the Master Unit) is the effective "God" of the verse.
- Lampshaded in Yu-Gi-Oh! The Abridged Series, although not quite true for the source material itself. Aside from their version of Ancient Egyptian mythology bearing only cosmetic resemblance to the original, later series have, among other things, the Aesir, who are basically the Norse God Cards.
- The SCP Foundation has quite a lot of objects that are obviously beings from Abrahamic Faith, but almost none for any other mythology.
- South Park combines this with All Myths Are True. Every god of every religion exists in the setting, but Mormonism is the only faith that gets you into Heaven (God himself is Buddhist). Everyone else goes straight to Hell, though it seems only real sinners actually get punished and everyone else is more or less left alone.
- In the episode "Best Friends Forever", that changed when they needed more soldiers to join in the battle against Satan's legion of Hell, and Mormons aren't fighters. Considering that it's South Park, things went back to the way they were, not that soldiers aren't needed.
- Hilda: the show relies heavily on Norse Mythology and Scandinavian folklore. However, there are a few creatures from other mythologies, such as a Thunderbird (Native American) and Barghest (English).