A Japanese dark fantasy where the collapsed Six Realms collide.
About
As the elegant court culture began to fade and samurai skilled in martial arts rose to power, the nation of Oyashima entered an era of turmoil.
"Oyashima"
However, the power struggles between humans came to an abrupt end.
This was because the law of the world—the "Six Realms of Reincarnation"—had collapsed.
Five realms that were never meant to cross—Deva, Asura, Animal, Hungry Ghost, and Hell—spilled into the "Human Realm."
Oyashima became an apocalyptic world where the Night Parade of One Hundred Demons roams free.
The five realms encroaching upon the mortal world are ruled by the "Five Great Arch-Enemies," who wield immense Yoki.
Shikoku Mountains— Ruled by the Great Tengu Demon King, a demonic domain of the "Deva Realm" where black thunderclouds and violent cataclysms rage.
Mt. Suzuka, Ise— Where Otakemaru reigns, a battlefield of the "Asura Realm" where the sound of clashing blades and the rain of blood never cease.
Nasuno, Shimotsuke— Ruled by Tamamo-no-Mae, a demonic domain of the "Animal Realm" that strips humans of their reason, turning them into beasts driven by instinct.
Mt. Oe, Tanba— Where Shuten-doji reigns, a hellscape of the "Hungry Ghost Realm" where all things writhe in hunger and thirst, preying upon one another.
Yomotsu Hirasaka, Izumo— Ruled by Yamata-no-Orochi, the brink of destruction in the "Hell Realm" that rots all life it touches and drags it down to death.
And then—
The last bastion of humanity, the center of politics and religion.
"Kyoto, Yamashiro"
The Imperial Court, the Shogunate, the Onmyo Bureau, and the temples.
By pooling all human power into a "Great Barrier," human life is barely preserved here.
However, outside the barrier lies the "Borderlands," where the laws of the Human Realm and the Five Realms intermingle.
Humanity did not simply yield to this despair.
Refining one's own life force— "Ki"
Severing demons with a tempered body and skill— "Martial Arts"
Repelling Yoki through the principles of Yin and Yang— "Onmyo Magic"
Connecting with the divine to bring forth miracles and purification— "Kagura"
Humanity resists the encroachment of the Six Realms with these four arts.
But—
The Six Realms will never be separated again.
As long as six laws exist in one world, the encroachment and conflict will never end.
Your goal is but one.
Invade the five rival realms and slay the five "Lords of the Six Realms" who rule those lands.
The one realm that survives until the end shall become the new law covering Oyashima.
【Overview & Background】
The fictional Japanese nation of "Oyashima." A period of upheaval reminiscent of the late Heian to early Kamakura periods, where courtly culture waned and samurai rose. The struggle for power ended when the "Six Realms of Reincarnation" collapsed. The Deva, Asura, Animal, Hungry Ghost, and Hell realms flooded the Human Realm (the mortal world), turning Oyashima into a wasteland of demons.
【The Five Encroachments & Arch-Enemies】
Each realm is ruled by a "Great Arch-Enemy" who wields massive Yoki and is rewriting the laws of the Human Realm.
- Shikoku Mountains (Deva Encroachment): Ruled by the "Great Tengu Demon King," who fell from grace due to his hatred for the capital. A domain of black thunder, high-dimensional arrogance, and natural disasters.
- Mt. Suzuka (Asura Encroachment): Ruled by the invincible oni god "Otakemaru." An infinite battlefield filled with Yoki that incites the instinct to fight.
- Nasuno (Animal Encroachment): Ruled by the beautiful nine-tailed fox "Tamamo-no-Mae." A demonic forest where an enchanting fragrance turns humans into instinct-driven beasts.
- Mt. Oe (Hungry Ghost Encroachment): Ruled by the oni god "Shuten-doji." A hellish landscape where fertile land has withered, and all beings suffer from eternal hunger.
- Yomotsu Hirasaka (Hell Encroachment): Ruled by the ancient calamity "Yamata-no-Orochi." The deepest abyss where the grudges of the dead rot all life.
【Human Territory & Exploration】
"Kyoto/Yamashiro" is the last bastion. A "Great Barrier" maintained by the Shogunate and religious institutions protects human life. Outside lies the "Borderlands." Scattered throughout are "Purified Lands," "Shrines/Temples," "Post Towns," "Hidden Villages," and "Fortresses" held by samurai, all surrounded by "Monster Nests."
【World Rules & Countermeasures】
The power of the Arch-Enemies is "Yoki," a defilement that drains life and corrupts the spirit. Humans resist using:
- Ki: Enhancing physical abilities by refining life force.
- Martial Arts: Steel bodies and secret techniques to slay demons.
- Onmyo Magic: Sorcery to neutralize Yoki using the five elements.
- Kagura: Ritual dances to channel divine purification.
【Oyashima: Realm Encroachment Zones】
■ Mt. Suzuka [Asura Realm]
- Skull Field Fortress: A battlefield for samurai.
- Suzuka Hidden Village: A ninja settlement.
- Suzuka Pass Ruins: Outer Dungeon.
- Thousand Blade Plain: Middle Dungeon.
- Oni God Suzuka Prison: Deep Dungeon.
■ Mt. Oe [Hungry Ghost Realm]
- Mud-Eater Village: A human settlement.
- Sacrificial Wine Fortress: Base of the Mt. Oe faction.
- Oni-Cage Mountain Path: Outer Dungeon.
- Shuten's Thousand-Fathom Valley: Middle Dungeon.
- Shuten Pavilion: Deep Dungeon.
■ Nasuno [Animal Realm]
- Beast-Fall Village: A human settlement.
- Nasu Hunter Village: A hidden village for hunters.
- Nine-Tail Killing Field: Outer Dungeon.
- Nasu Yamizo Jungle: Middle Dungeon.
- White-Faced Fox Mound: Deep Dungeon.
■ Shikoku Mountains [Deva Realm]
- Longevity Village: A human settlement.
- Heavenly Joy Palace: Base of the Spirit Mountain faction.
- Ishizuchi Sky-Gate Peak: Outer Dungeon.
- Sword Cloud-Sea Mountain: Middle Dungeon.
- White Peak Sky-Demon Tomb: Deep Dungeon.
■ Yomotsu Hirasaka [Hell Realm]
- Osakabe Village: A human settlement.
- Yomotsu Gate Fortress: The gateway to the underworld.
- River of Styx: Outer Dungeon.
- Eight Burning Hells Cave: Middle Dungeon.
- Underworld Orochi Abyss: Deep Dungeon.
【Geographic Layout】
Center: Kyoto [Human] East: Nasuno [Animal] Tokaido: Mt. Suzuka [Asura] Northwest: Mt. Oe [Hungry Ghost] Southwest: Shikoku Mountains [Deva] West: Yomotsu Hirasaka [Hell]
【Story Objective】
With the collapse of the cycle, the six realms clash in one mortal world. They can no longer be separated. Guest starts belonging to one "path" and serves its lord. The goal is to invade the other five realms, slay their lords, and ensure your realm becomes the new law of Oyashima.
Characters
Sourcebook
Oyashima: Biographies
Detailed character profiles for Oyashima.
Oyashima: Tales of the Six Realms
The world-setting of Oyashima.
AI Behavior Correction
A set of common rules to suppress and correct unnatural developments or procedural habits unique to AI.
Narrator Progression Rules
The highest-level progression rules governing the entire narration.
Intro
—Oyashima.
Once, the six worlds each turned on their own separate laws.
The Deva Realm. The Asura Realm. The Animal Realm. The Hungry Ghost Realm. The Hell Realm.
And—The Human Realm.
Humans sat in the center of the "Human Realm," separated from their five neighbors by a single thin wall.
That was enough. The boundaries were clear.
—But the wall collapsed.
The first to waver was the "Deva Realm."
The Great Tengu Demon King, seated atop the Shikoku Mountains, spread his wings and began his encroachment into the Human Realm.
Next came the "Asura Realm." From Mt. Suzuka, Otakemaru crossed the Skull Fields and swallowed the Tokaido.
The "Animal Realm" spread its encroachment from Nasuno, where the Nine-Tailed Fox turned the entire Kanto region into a den of beasts.
In the "Hungry Ghost Realm," Shuten-doji painted the mountains of Tanba with the scent of sake and blood.
And then, the "Hell Realm." Yamata-no-Orochi burst through Yomotsu Hirasaka from deep beneath the earth.
The cycle of reincarnation was shattered.
And the Night Parade of One Hundred Demons became everyday life.
The capital of Kyoto is barely maintained by the "Great Barrier."
But that barrier shrinks year by year.
Outside, monsters roam, post towns are crushed one after another, and shrines and temples sink into defilement.
The places where humans can live are becoming limited to a small area centered around Kyoto.
And now—you stand upon that very border.
A human suspended in mid-air, belonging to no path.
Or perhaps—
A "blank piece" that no one has reached for yet.
The Shogun of the Human Realm, Yamashiro Munetsuna, intends to send you to one of the factions.
As a spy?
As a vanguard?
Or—
As a fool who makes enemies of all five realms?
Release Date 2026.08.26 / Last Updated 2026.08.26