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

This AU has no further presence online than this page.

For information to establish this AU's online presence, see the Template AU Page.

AfterWorld is an eldritch, sci-fi, hellish AU based around the future - and the collapse - of our solar system, and each world's change influencing the physical form of all of the monsters. The AU begins after Chara possesses humans that fall into the Underground, resetting the world after each genocide run. The resets create changes and anomalies that cause the CORE to eventually collapse and explode, which spreads out and corrupts the monsters, transforming them into terrifying beasts. Frisk is born 6.5 billion years into the future on Mars, now terraformed and renamed to "Solitude," and moves to Earth to explore, causing the story to unfold.

Character Changes

Undertale Characters

Frisk, The Eighth Fallen

A human born 6.5 billion years from today, she is slightly timid and usually very forgiving of others. She's very protective of Chara, but dislikes fighting and does not do it very often.

Chara, Shattered Scapegoat

After being killed by Sans 37,047,734 times, and accidentally breaking the world, she has been deprived of her ability to reset, and now regrets her genocide option. She now only wants forgiveness, which she does not expect from anyone. As the story progresses Chara starts to grow very attached to Frisk.

Sentinel, Blazing Malice

Left to burn on Venus, he has gotten much larger and more dangerous. His eye sockets have melted into one, with a glowing red eyeball in the center. He has a massive hole and several cracks in his skull, lots of very sharp teeth, and his jacket is withered and torn.

Poltergeist, Apparition of the Inferno

Also abandoned on Venus, he has changed dramatically. He resembles a leg-less, demonic, faceless, almost phantom-like skeletal creature, with a massive red eye in his mouth and two in his hands, like Gaster's.

Plaguebringer, Floral Amalgamate

An amalgamate of most of the Ruins' monsters, Plaguebringer is a devilish, face-less, multi-eyed flower with a thirst for killing. It was awakened shortly after Frisk first entered the Underground. Plaguebringer does not contain the essence of Asriel, they are two separate entities.

W.D. Gaster, Vengeance of the Void

The only Royal Scientist to have survived the catastrophic collapse of the CORE, and one of the only monsters to have remained on Wasteland. After one of the RESETS, the timeline was altered where Gaster never fell into the CORE, only to be later killed by Chara. In one of the following RESETS, the timeline was altered again where a prototype blaster experiment goes horribly wrong, fusing the blaster with Gaster's own head. After the collapse of the CORE, billions of years from now he regained consciousness just after Frisk fell into the Underground.

-- The remaining monsters will be revealed as the AU develops. --

Additional Characters/Species

The Ebonmorphs

Billions of years ago, when Demise was habitable, the dominant species were a carnivorous, canine-like race now known as the Ebonmorphs. They were large, almost ten meters in length, and were covered in a coat of dark, indigo fur. When Demise began to grow uninhabitable, due to excess amounts of greenhouse gases emitted into the atmosphere via volcanoes, the Ebonmorphs began dying out, and went extinct long before humans evolved.

Due to unknown causes, the collapse of the CORE transformed Papyrus into an Ebonmorph skeleton, severing its lower body and granting the new creature the ability to hover above the ground.

The Devorothoths

Also nicknamed the "Devourers", the Devorothoths are an ancient, almost Lovecraft-like race of titanic, eldritch monsters that roamed and lived in the vacuum of space. They are among the largest biological entities in the galaxy, with fully-grown adults extending hundreds of kilometers long. These creatures will devour anything that strays too close, from space probes, spacecraft and space stations to even entire asteroids and comets.

There is no clear answer to where these beasts originate from, although from trace evidence gathered by space probes the most accepted theory is that these creatures were once a single, living planet, that shattered long ago, separating into these creatures that spread across the galaxy like jet fuel.

Location Changes

This AU does not take place entirely in the Underground, and expands throughout the Solar System.

Undertale Locations

Most of the Underground has been rendered uninhabitable, primarily because most of it no longer exists. After the Moon collided with Earth, shockwaves from the impact sent earthquakes of unimaginable power across the planet, and causing part of the Underground to collapse into a ravine that stretches hundreds of kilometers down. This chasm has been renamed to the "Void," and makes up more than 90% of the Underground's surface area.

Parts of the Underground still standing are the Ruins and New Home. Parts of the Ruins have been degraded and/or have caved in, but Toriel's house is mostly intact.

The Barrier is still standing, but not for long. Billions of years of wear and tear have degraded the Barrier, and it has grown far weaker.

Additional Locations


  • Analogue: The Sun
  • Radius: 94,200,000 km
  • Type: Red Giant Star

Once a small, golden yellow star that gave life; now it has expanded and is a deep crimson color. It has entered its Helium Flash, the stage in which it has begun fusing helium into carbon and oxygen in its core. It has also already consumed the planet Scorn.

Scorn (Destroyed)

  • Analogue: Mercury
  • Radius: 2,128 km (before destruction)
  • Semimajor Axis: N/A
  • Type: N/A
  • Terrain: N/A
  • Special Features: N/A
  • Inhabitants: N/A

Once the innermost planet, Scorn has been annihilated by the ever-expanding Archangel. Most of the planet's crust had already been strip-mined in a failed attempt to construct a Dyson Sphere around Archangel.

-- More description will be added as the AU develops, to avoid spoilers. --


  • Analogue: Venus
  • Radius: 5,924 km
  • Semimajor Axis: 103,000,000 km
  • Type: Terrestrial Planet
  • Terrain: Molten, Volcanic
  • Special Features: Pillars of Judgement
  • Inhabitants: Sentinel, Poltergeist

After 6 billion years, it has remained the hottest planet in the solar system. This world has been stripped of its atmosphere, and the tidal forces of Archangel have broken and melted the planet's crust.


  • Analogue: Earth
  • Radius: 6,408 km
  • Semimajor Axis: 165,000,000 km
  • Type: Terrestrial Planet
  • Terrain: Irradiated Desert, Ruins, Mountains, Salt Plains
  • Special Features: Mt. Ebott
  • Inhabitants: Chara, Plague, W.D. Gaster, ???

Once the home for humanity and monsterkind, now a barren, yellow desert. Its moon collided about 100,000 years ago, resulting in a molten red ring to form around the planet.


  • Analogue: Mars
  • Radius: 3,485 km
  • Semimajor Axis: 224,000,000 km
  • Type: Terrestrial Planet (Terraformed)
  • Terrain: Grasslands, Forests, Deserts, Tundra, Oceans, Urban Sprawl
  • Special Features: Valles Marinares
  • Inhabitants: Humans, ???

The current homeworld for mankind. It has been terraformed into a lush, Earthlike planet, and its moons were destroyed in the terraformation process. Frisk grew up in a rural, sparsely populated area of Solitude, but she eventually migrated to one of the central cities near Valles Marinares, where she escaped Solitude as a Wasteland scavenger.


  • Analogue: Ceres
  • Radius: 919 km
  • Semimajor Axis: 413,000,000 km
  • Type: Dwarf Planet
  • Terrain: Barren
  • Special Features: ???
  • Inhabitants: ???

The largest of the asteroids in the Asteroid Belt, Graveyard is a lifeless, barren rock. [More description TBA]


  • Analogue: Jupiter
  • Radius: 72,013 km
  • Semimajor Axis: 779,000,000 km
  • Type: Jovian Planet
  • Terrain: Gas
  • Special Features: ???
  • Inhabitants: ???

The monstrous gas giant of the solar system, wrapped in thick bands of white, gold, brown, and black clouds and whirlpools. Several of its moons have either collided with each other or the planet itself, but a few remain possible future homes for humanity.


  • Analogue: Io
  • Radius: 1,827 km
  • Semimajor Axis: 419,000 km
  • Type: Terrestrial Moon
  • Terrain: Frozen Sulfides, Volcanoes, Sulfur Lakes
  • Special Features: ???
  • Inhabitants: ???

A frozen, volcanic, sulfur-covered hell, it's amazing Expanse has survived the calamity of events that have destroyed most of Reaper's moon system. The radiation from Reaper's magnetosphere has caused many different breeds of strange, alien life to inhabit this bizarre world.


  • Analogue: Europa
  • Radius: 1,553 km
  • Semimajor Axis: 671,000 km
  • Type: Terrestrial Moon
  • Terrain: Ice, Ravines
  • Special Features: ???
  • Inhabitants: ???

One of the few surviving moons of mighty Reaper, Narcosis has evolved from a frozen wasteland to a world almost completely covered in water. Archangel's helium flash has breathed new life to this alien world, but one should take great precautions before descending into the abyss...


  • Analogue: Saturn
  • Radius: 60,428 km
  • Semimajor Axis: 1,518,000,000 km
  • Type: Jovian Planet
  • Terrain: Gas
  • Special Features: ???
  • Inhabitants: ???

Once the jewel of the solar system, Isolation has long since lost its magnificent rings, and is now a large, bland, pale yellow sphere. Its moon system, like Reaper, is also beginning to collapse.


  • Analogue: Rhea/Titan
  • Radius: 2,893 km
  • Semimajor Axis: 1,038,000 km
  • Type: Terrestrial Moon
  • Terrain: Ice, Lava Fields, Chasms
  • Special Features: ???
  • Inhabitants: ???

After a deadly collision between the moons Rhea and Titan, the ice of Rhea mixed with the natural gases of Titan, igniting both moons into an inferno that has never fully subsided. This new world, Abhor, stands as a warning to all worlds in the Archangel system; the worst is yet to come.


  • Analogue: Uranus
  • Radius: 25,962 km
  • Semimajor Axis: 2,857,000,000 km
  • Type: Cryojovian Planet
  • Terrain: Gas
  • Special Features: ???
  • Inhabitants: ???

A pale blue gas giant long since ridiculed for its previous name, a voyage to Gemini is no laughing matter. Its moon system has degraded heavily, leaving very few survivors.


  • Analogue: Miranda
  • Radius: 218 km
  • Semimajor Axis: 127,000 km
  • Type: Terrestrial Moon
  • Terrain: Ice, Crags, Ravines
  • Special Features: ???
  • Inhabitants: ???

Over the eons, Gemini's moon Labyrinth has been broken apart and smashed to pieces, only for gravity to pull the debris back into a solid moon. Parts of the moon's insides now cover the titanic mountains and abyssal canyons and valleys, creating a vast, interlocking cavern network that stretches deep into the moon.


  • Analogue: Neptune
  • Radius: 23,482 km
  • Semimajor Axis: 5,231,000,000 km
  • Type: Cryojovian Planet
  • Terrain: Gas
  • Special Features: ???
  • Inhabitants: ???

The twin world of Gemini, Covenant has destroyed its major moon Triton eons ago, and has drifted into the Kuiper Belt. There, it captured the lonely dwarf planet Rend, forcing it into orbit.


  • Analogue: Eris
  • Radius: 1,128 km
  • Semimajor Axis: 419,000 km
  • Type: Terrestrial Moon
  • Terrain: Frozen, Geysers
  • Special Features: ???
  • Inhabitants: ???

This frozen world used to float adrift in the outer fringes of the Kuiper Belt, but due to the powerful gravity of Covenant, the object was pulled out of its orbit and into an orbit around the ice giant. Covenant had recently finished annihilating its previous largest moon, Triton, but Rend orbits far enough away to avoid orbital decay, at least for now.


  • Analogue: Pluto
  • Radius: 1,192 km
  • Semimajor Axis: 5,932,000,000 km
  • Type: Dwarf Planet
  • Terrain: Frozen
  • Special Features: ???
  • Inhabitants: ???

As Archangel continues to grow, its habitable zone will expand further and further into space. This lonely, small, icy moon will be mankind's last home orbiting Archangel, before leaving it behind and plunging into interstellar space. A research settlement used to exist on Terminal, but due to unknown circumstances, communication with the outpost has ceased. Just before communication cut-off, scientists reported unusual seismic activity from beneath the base, followed by an in-human howl...


  • Analogue: Planet Nine
  • Radius: 19,865 km
  • Semimajor Axis: 7,148,000,000 km (orbit highly eccentric)
  • Type: Cryojovian Planet
  • Terrain: Gas
  • Special Features: ???
  • Inhabitants: ???

The true ninth planet. Over billions of years the orbit of this frozen ice giant has decayed, bringing it closer to Archangel, and causing scorn and discord as it flings asteroids and comets randomly, hitting the inner planets and moons. Seraph is classified as a Y-class brown dwarf, glowing deep crimson in color. The "planet" orbited by five "moons", one of which has been given the name "Nibiru", after the supposed doomsday planet proposed by early, primitive humans.


Story Explanantion

After the events leading up to the death of Asriel and Chara Dreemurr, and Asgore declaring war once again on the humans, Chara posessed the next human that fell into the Underground. With a new body, she proceeded to kill off every monster within the Underground, combining her Determination with the Determination of the child she possessed. After her successful genocide, she RESET the world, which caused minor fluctuations and anomalies.

She then possessed the child that fell into the Underground again, and repeated the process five more times. After her sixth RESET, the CORE became dangerously unstable, causing it to go into meltdown. The CORE collapsed and exploded, causing a rupture in the fabric of space-time, and corrupting the entire Underground. Due to a series of mysterious and unexplained events, Chara also lost the ability to RESET, and lives in the hollow husk of a ghost-like body. Fearing revenge by the other monsters, she fled to hide deep within the remains of the Ruins.

The monsters' physical forms were altered - and in some forms enhanced - and distributed across the solar system, left to wander aimlessly across their new home.

Soon after the collapse of the CORE, humans began expanding outward to colonize the other worlds of the solar system, one of which being Venus. Despite the crushing pressure, acidic rain, and extreme heat, a colony was established. Unfortunately, Sentinel and Poltergeist, now filled with scorn for humans, attacked the human settlement. All of the colonists were killed in the attack, and no human has set foot on Venus ever since.

Six and a half billion years later, the Sun became dangerously low on fuel, and began its death throes. Its core was now more than five times hotter than it once was, beginning a cycle called the "Helium Flash," where it rapidly starts fusing helium into carbon and oxygen. This caused the Sun to swell up, transforming it into a red giant. In its expansion, it annihilated and consumed the planet Mercury, now called "Scorn".

Around the time the Sun - now called "Archangel" - grew to almost the size of Venus's orbit, Frisk was born. She grew up to become a Wasteland scavenger, part of a team that searches for ancient artifacts beneath Wasteland's surface. Unfortunately, soon upon landing, the crew encountered a meteor storm that destroyed the mine, and caused Frisk to fall into Mount Ebott.

-- Story will be added as the AU develops, to avoid spoilers. --



  • Although similar, AfterWorld is not based on the AUs Underworld or After!Tale at all.
    • It's name is based on the concept "After our world," and is set long after our once beautiful blue world has been turned inhospitable and abandoned.
  • Each of the planets' new names correspond to its relationship with other planets, or Archangel. For example, Venus has been renamed to "Demise" because of its impending destruction by the expanding red giant.
  • Most of the monsters in AfterWorld are tall, or otherwise extremely large.