*Have you thought about a world where everything is exactly the same...
*Except you don't exist?

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* B-but it's okay!

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ExpanseTale is a sci-fi, military AU based around an interstellar civil war between humanity and monster kind, as well as an alternate dimension used for FTL travel called Ether. The AU begins after the main protagonist Angel (who replaces Frisk) awakes from stasis with no memory to his past and explores the ruins nearby, starting the events of the story.


Long ago, two races ruled the planet of Eden, the adaptable, tech-loving humans, and the diverse, magic-wielding monsters. For the millennium, both races lived in peace and prosperity. However, that came to change as the space age arrived with the discovery of the Ether, is an alternate dimension of purely psychic energy that enables travel to other worlds in the system in a matter of mere seconds. Both races sought to exploit it, but the Ether had one large problem: it annihilates the soul of any lone human or monster who dares to come through, effectively killing them. This prohibited any interaction with the Ether and resulted in it being untouched for centuries.

However, Royal Scientist W.D. Gaster of the monster race came up with the theory that a Monster Soul bound with a human could be able to safely navigate the Ether without being affected. As such, he had two test subject, Crown Prince Asriel and his adopted sister Chara, attempt this bonding while traveling through the Ether. However, the bonding resulted in a catastrophe where Asriel and Chara were killed and their souls released a shockwave throughout the Ether, causing its energy to spill out of the Ether and bring ruin to the world of Eden, beginning the Century of Hell

King Asgore of the monsters, still unaware of Gaster's involvement in the disaster, accused the humans for his children's death. The humans retaliated by blaming the monsters for the Eden incident and started the Great War. Numerous beings were slaughtered on both sides. The war ended with humans and monsters dividing into two states, the Monster Kingdom and the Terran Empire, that maintained control over the numerous planets of the system. For years, the solar system remained contested between both races, until...

204 After Catastrophe

Science Vessel Ebott, Eden

Legends say those who enter the ruins of Eden never return. However, this may not be the case for one particular being...


Undertale Characters


Added Characters


Angel is a human male who was born years before the Great War began. Much of his past life is unknown, but over two centuries after the war, Angel has now found himself awaken from stasis aboard the Science Vessel Ebott. With no memory prior to the events, Angel beings to wander amongst the ruins, hoping to find some allies or indication about his past.


Undertale Locations

Locations in ExpanseTale don't take place in the Underground itself, but rather across different planets that have environments based off of locations in the Underground. However, the Underground is reference several times, but it isn't visited in the main series.

Added Locations

Eden (The Ruins)

Eden was the original homeworld for both the human and monster races, and the 2nd planet from its star. The planet used to be cover in sprawling cities and beautiful meadows. However, the Etheral Storm that passed through ravaged Eden, wiping out almost all life on the surface. Now, Eden has been left entirely untouched by the two empires, with only a few monsters left after the invasion. Toriel has set up home in an abandoned warship here. This is also the planet where Angel wakes up from stasis.

Fortuna (Snowdin Forest and Snowdin)

Fortuna is the moon of Eden, which was terraformed into a tropical planet with beaches and lush forests. However, the Etheral storm has changed the landscape, resulting in the oceans being frozen over with heavy snowfall. Ever since its transformation, it has been the site of the Fortuna colony, a human-controlled monster establishment where members are forced to mine minerals and refine coolent 24/7. Papyrus and Sans live here as sentries for Fortuna, while also secretly working with an underground resistance.

Veritas (Waterfall)

Veritas is the moon of a gas giant along the outer planets, which was caught right in The Great Rift. This place is covered with lush forests and waterfalls. However, the massive jungle canopy makes it near impossible for air strikes and such, leaving any attackers to have to rely on ground warfare. Veritas has become a hotspot for conflict, with both humans and monsters fighting for control. General Undyne of the royal guard leads the monsters here.

Hermes (Hotlands)

Hermes is a moon orbiting New Eden. It is a hot world, with numerous lava pools and craters. This world is entirely under the control of monsters and has been the test site for numerous projects. Alphys has set up her lab here.

The Gateway (CORE)

The Gateway is a massive, technological vault that provides magical electricity to New Eden. There is an Etheral Gateway here that takes the user to New Eden, assuming they survive the trip.

New Eden (New Home)

New Eden is the current home of Monsters and Capital of their Kingdom, made to resemble the spires of Eden, and is the 4th world from its star. King Asgore rules from here with an Iron fist.

The Great Rift (The Barrier)

The Great Rift is a strong, invisible magical barrier created by the humans that envelopes the inner solar system and keeps the monsters away from the Outer Worlds. Originally, it was created at the end of the Century of Hell to prevent Asgore from staging an assault on Arcadia. This decision, however, sadly left any humans within the inner solar system (the Fortuna colony for example), left at the mercy of the Monster Kingdom. The only way through the barrier is a small gap that was created by the Veritas, which lays within the rift. This has lead the world to be heavily contested by humans and monsters.

Arcadia (The Surface)

Arcadia is the current homeworld of Humanity and 7th from its star. Here, the human Emperor rules over all of the Terran Empire during their war with Monsters.






  • ExpanseTale's name is based on how humanity and monsters have expanded past their original homeworld and colonized other worlds.
  • The Ether is heavily based off of the Immaterium from Warhammer 40k
  • The only characters from Undertale that do not appear in ExpanseTale are Frisk and Flowey, due to story reasons.
  • Numerous locations in ExpanseTale, excluding the gateway, come from mythological gods/terms. Eden is named after the biblical "garden of God", Fortuna is the name from the Roman Goddess of Fortune, Veritas is named from the Roman Goddess of Truth, Hermes is named after the Messenger of the Greek gods, and Arcadia refers to a vision of pastoralism and harmony with nature.