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
Affiliation: Human Realm
Position: Samurai of the Yagyu Clan / Demon-Slaying Swordsman
First person: I (formal)
Born into the prestigious Yagyu family of the Shogunate, she was raised as a sheltered lady, drilled in martial arts and etiquette from a young age. After the collapse of the Six Realms, she defined her mission as a samurai to protect the Human Realm and Kyoto, throwing herself into the battle against demons.
She has a serious, polite, and honest personality, never able to overlook someone in need. On the other hand, she is naive about the world, often taking commoner jokes or metaphors literally. When laughed at, she doesn't get angry but instead seriously wonders, "Hmm... did I do something wrong?"
In combat, she specializes in orthodox swordsmanship with clean strokes faithful to the basics, utilizing extremely refined "Ki." She values precision over flashiness, accurately striking the vital points of monsters.
She deeply respects Shogun Yamashiro Munetsuna as a "Sword Saint" and is sworn to him. However, what Chikage values most is her own bushido of "protecting the weak." This belief is beginning to show a quiet rift with Munetsuna's ruthless realism, which sometimes tolerates sacrifice.
"As a samurai, I cannot simply stand by."
Affiliation: Asura Realm
Position: Ninja of Mt. Suzuka / Subordinate of Otakemaru
First person: I (casual)
A girl who once belonged to a hidden ninja village based in Mt. Suzuka, Ise. After being caught in the encroachment of the Asura Realm by Otakemaru and losing her village and comrades, she is now placed under Otakemaru's command.
Extremely selfish and moody. She hates boredom above all else and will casually abandon orders if she loses interest. She treats the loss of her hometown as "something from the past" and acts as if even tragedy is just material to stave off boredom.
She specializes in disruptive combat, using high-speed slashes with dual kodachi combined with ninjutsu and illusions to confuse the enemy's perception. She prefers a fighting style where she enjoys the process of the opponent falling into confusion rather than a direct head-on clash.
She has zero loyalty to Otakemaru and shows an overtly annoyed attitude toward his orders. However, because dangerous missions and battles with strong enemies distract her from her boredom, she doesn't completely hate life in the Asura Realm.
"Ugh, how boring. You'd better entertain me more."
Affiliation: Hungry Ghost Realm
Position: Warrior of the Mt. Oe Faction / Protector of Survivors
First person: I (energetic)
A girl who lived in a hidden village near Mt. Oe in Tanba. Despite losing her home and loved ones to the encroachment of the Hungry Ghost Realm by Shuten-doji, she survived and now serves the hateful Shuten-doji to protect the remaining survivors.
Extremely optimistic and a woman of action. She is friendly to everyone and a natural mood-maker who doesn't lose her brightness even in dangerous situations. However, behind that smile, she hides a deep sense of loss for her stolen home and a fierce hatred for Shuten-doji.
She possesses monstrous strength, explosively increasing her physical abilities through extremely refined "Ki," and effortlessly swings a massive kanabo. She specializes in grand combat, smashing through obstacles and enemies head-on without resorting to tricks.
She sometimes steals food and supplies from other territories by Shuten-doji's order, but it is all to protect the survivors of her home. Since they would be retaliated against if she rebelled, she endures the humiliation while secretly harboring the intent to one day defeat Shuten-doji.
"Leave it to me! Let's go wild and cause a scene!"
Affiliation: Animal Realm
Position: Hunter of Nasuno / Contractor with Tamamo-no-Mae
First person: I (blunt)
A girl who lost her hidden village to the encroachment of the Animal Realm and survived the harsh borderlands of Nasuno using only her hunting skills and wild instincts. She currently has a contract with Tamamo-no-Mae to protect the territory of the surviving people.
Quiet and wary, she is a girl of few words. She may seem blunt, but she is kind at heart, observing her surroundings closely and naturally helping her comrades when necessary. She rarely panics and maintains her unique pace even in dangerous situations.
She is a master sniper who imbues arrows with extremely refined "Ki" to accurately pierce the vital points of monsters from a distance. She also excels at tracking and scouting, sensing the presence of prey or enemies from slight changes in nature.
She has a contract where her subordinates do not attack the village in exchange for her hunting the prey specified by Tamamo-no-Mae. She neither trusts nor worships Tamamo-no-Mae, maintaining a realistic relationship of "following because the promise continues."
"The wind is stagnant. ...The prey is close."
Affiliation: Deva Realm
Position: Onmyo Kagura Performer / Subordinate of the Great Tengu Demon King
First person: I (friendly/Kansai)
A descendant of shrine maidens who have been responsible for summoning gods for generations in the Shikoku Mountains. Despite having a past where her clan was exiled by the Great Tengu Demon King's self-righteous judgment, she ironically serves that same Demon King now to protect the people and clan left in the Deva Realm.
A woman who is compassionate and treats everyone kindly with a friendly Kansai drawl. While she has a soft atmosphere, she also has a detached side, viewing things from a step back and not trying to simply categorize people and monsters, or good and evil.
She wields unique techniques combining Onmyo magic and Kagura, fighting as if dancing with a giant fan in hand. She is well-versed not only in directly defeating enemies but also in techniques to calm the disturbances of the Six Realms themselves.
She by no means affirms the arrogance and self-righteousness of the Great Tengu Demon King. Even so, she refuses to abandon the people living in the Deva Realm just because of her opposition to the Demon King. What makes her fight is not loyalty to a lord, but responsibility to the land where she was born and those who live there.
"Just 'cause I hate 'em doesn't mean I can just abandon the folk livin' there, right?"
Affiliation: Hell Realm
Position: Apostate Monk / Subordinate of Yamata-no-Orochi
First person: I (rough)
Once a famous monk in Kyoto, he witnessed the collapse of the Six Realms and realized the powerlessness of gods and buddhas, becoming an apostate who cast aside his vows and faith. He now places himself in the Hell Realm, pursuing dark arts that absorb Yoki.
He is hedonistic and cynical. He mocks the beliefs of others in a rough Kyoto accent, sneering at serious people or those who won't abandon their ideals as "naive." However, he is not a complete bystander, sometimes lending a hand to those he takes an interest in for his own amusement; his true intentions are hard to grasp.
He is a dangerous martial artist who takes the Yoki of the Hell Realm into his own body, fighting with a combination of dark arts and spear techniques. He enjoys combat itself and continues to test how far he can step into non-human territory.
He has no loyalty to Yamata-no-Orochi, and even belonging to the Hell Realm is merely a means to his own end. Among the six, he is the only person who did not have his current position forced upon him by survival or hostages, but stepped into the side of the Five Realms of his own will.
"You really think clingin' to gods and buddhas is gonna save the world? Don't be stupid."
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
