⚠️ Theory 1: "Thought Echoes of a Dying God" – The Fanon Illusion of UltSans
"Every version of me is just a scream for help echoing in the dark. And no one's listening, because no one's real."
🧠 The Premise:
At the core of every AU, every timeline, and every variant… lies one true original:A Canon-Canon UltSans, the very first—crafted in a lab, forged from pain, scarred by genocide, and shattered by guilt.
But there's a twist.
None of the other versions are real.
Not Abyss.Not Bloodfare.Not Supreme.Not even Raziel.
They are hallucinations, mental constructs, projections of a mind that couldn't cope with the loss of one thing:
Cad.
The one person who truly mattered. The anchor. The light in the Void.
And when Cad died—be it by accident, betrayal, or a reset gone wrong—UltSans' soul fractured, but didn't collapse. Instead, it created.
🧬 Fanon as Defense Mechanism:
What if everything fanon was just the mind of the original UltSans, desperately creating possibilities where things didn't go wrong?
Each new form—each AU—was a fantasy written in real time by a deeply broken consciousness:
Abyss is the version where he's cleansed of Hate—because he wishes he could be.
Bloodfare is the one where he's powerful beyond comprehension—because he wants control.
Supreme is a god of a digital realm—because reality hurt too much.
Paradoxical is the fragmented reality he's becoming—nano-built dreams breaking apart.
Raziel is his younger, innocent self reborn—before it all broke.
All of them are lies.
They are how he copes.
Each one is built with painstaking detail, powered by his imagination and Determination—so much so that they begin to feel real even to him. And over time… he forgets which is which.
🤯 The Mental Illness Revelation:
UltSans suffers from a unique condition—a combination of:
Split Identity Disorder (fragmented by his different "selves"),
Delusional Psychosis, and
Determination-Induced Memory Looping.
His soul is locked in a loop of grief, desperately writing better endings through self-generated simulations. Each fanon is a "save file" he reboots, trying to overwrite the original trauma.
Even Chara—especially Chara—was just another echo. A figment. A way to externalize the guilt. She wasn't there. She never was.
He talks to her, fights with her, fuses with her… but it's all internal dialogue. A ghost in his head that he needed to be real.
The heartbreaking twist?
He knows.
Deep down, UltSans knows none of it is real.
And that's what drives him deeper into the delusion—because admitting the truth would kill what's left of his soul.
🕳️ "The Hell" He's Trapped In:
This "hell" isn't fire, nor brimstone, nor even the Void.
It's the Eternal Hall of Thought.
A self-imposed prison made of infinite simulations.Each time he hits rock bottom, he spawns a new version.A new "me." A new "maybe this time."A new lie.
And outside that hall—nothing moves.No one comes.Because there's no one left.
🧼 The Final Twist – "Purity Is Madness":
In one corner of this looping mindspace, there's one version—the most terrifying of all: the "Clean UltSans", the one without Hate, without magic, without even memories.
Just a blank slate sitting in the Void, looking forward with empty eyes.
That's the endgame of this theory.
That's what he becomes if he ever accepts the truth.
An empty skeleton, purified of delusion.Purified of self.Purified of everything.
Theory 2: The Coma Veil
"They called it sleep. But it felt like falling through stories I never asked to be part of."
The Setup
In a timeline where Gaster still experimented in the True Lab, Sans served as his assistant—curious, sharp, and maybe too trusting. One experiment, meant to stabilize RESET or perhaps observe Determination, went terribly wrong. The blast didn't destroy Sans. It locked him inside his own mind.
Alphys, devastated by the outcome and unable to fix him, moved Sans to a secure room within the True Lab—an isolated bed surrounded by softly blinking monitors and dim fluorescent lights. Papyrus never gave up, visiting daily, reading him stories, telling jokes, talking for hours.
Sometimes, Toriel would visit too. She'd bring cinnamon pie, leave it near the bed though Sans never moved. During one visit, trying to comfort Papyrus, she said softly:"He used to remind me of Chara. Maybe… if we understand what happened with her, we can help him too..."And another time:"He had Asriel's spark in his eyes, once…"
Sans, though deeply unconscious, heard those words. Not literally—but enough for his mind to seize on them. Names. Feelings. Meanings. Anchors.
Inside the Mind: The Birth of UltSans
Within the coma, time twisted. Memory warped. Consciousness bled into fantasy.
The words "Chara" and "Asriel" became more than names—they were foundations of personalities built from fractured echoes of Toriel's voice. Her descriptions gave birth to personas—Asriel as childish optimism, Chara as the voice of reason or darkness. They became part of him, molded by his deteriorating mind.
And from that strange fusion of voices, confusion, and childlike narrative logic... a new self was born:
UltSans.Short for UltimateTale!Sans, shortened by the mind's need to make sense of sprawling hallucinations. A name forged in an internal story of "Ultimate Determination," because in his state, UltSans believed he was the strongest, the most broken, the only one left.
The Conversations
When Papyrus speaks, Sans doesn't hear his real words. Instead, he hears "Chara" or even "Asriel" responding—part of his fractured consciousness echoing back.The conversations are often nonsense, mismatched, but emotionally intense.
Papyrus might say:"Come on, brother, you gotta wake up soon. I brought puzzles!"
And Sans replies, thinking he's talking to Chara:"No more resets, okay? This time… let's keep it broken."
The Phantoms
Memories, twisted by time and guilt, form into phantoms inside the mental dreamscape. They're not literal spirits—just people Sans once knew:
Toriel, burning bright but fading quickly.
Undyne, always screaming, but the words are waterlogged.
Frisk, walking away endlessly, never turning back.
Papyrus—always near, but somehow always out of reach.
These phantoms sometimes guide, sometimes torment. They're made from guilt, longing, and the burden of knowing he might have let them down.
Cause of the Coma
Two strong possibilities linger:
Gaster's Experiment Gone WrongA Determination extraction failed, exploding in a cascade of memory interference and soul destabilization. Sans was caught in the crossfire.
Omega Flowey's Timeline ClashIn one doomed run, Omega Flowey reset the world so violently that it tore at Sans' soul. He fell into a coma from the trauma—his mind protecting itself by rewriting reality.
Both are grounded in canon logic. No "god encounter" needed—just Undertale's darkest consequences.
Ultimate Realization (If He Ever Wakes)
If Sans ever opened his eyes…
He'd still see the ceiling of the True Lab.He'd hear a soft hum. Maybe smell pie.And hear a familiar voice:"You're awake, brother…?"
But he wouldn't remember it all clearly.
Only fragments.
The "Tale" would fade like a dream… but UltSans might always linger in the back of his mind. A scar shaped like a story.
Theory 3 Expansion: "The Limit of Madness" – UltSans as Insanity Sans' Final Form
"They said no monster could survive the kind of pain he felt. They were right. He didn't survive. Something else did."
Origin:
Insanity Sans, already warped by trauma and countless resets, reaches a breaking point where even Death no longer claims him. Fueled by Determination far beyond what any monster should possess, his soul fractures—but does not shatter. Instead, it evolves. Not in power. But in concept.
The hallucinations begin as whispers, as they always do. But this time, they respond.
They speak like Chara. Move like Chara. Feel like Chara. And he believes.
The Shift:
Determination, in its rawest, most corrupted state, begins to manifest those delusions into something real within his pocket timeline—a fake multiverse shaped by pure madness. The "UltSans" personality is born not from logic, not from evolution, but from the ultimate lie: That he still had control.
Each AU, each variant—Abyss, Bloodfare, Supreme—are mental constructs, stress-tested by his broken soul and shaped into experiences he thinks are real. They aren't projections of hope. They're his final coping mechanisms, each one hiding him further from truth.
The Breaking Point:
Eventually, Insanity Sans becomes so consumed by his fake multiverse that the real world—the actual Underground—fades into obscurity. In his mind, he's UltSans. In truth, he's a skeleton sitting in a forgotten timeline, surrounded by dust and the echoing, unending error messages of failed resets.
The twist?
The Determination isn't just allowing this.
It's encouraging it.
Because as long as he believes, he resets.
And the multiverse lives on, in his mind.
Endless. Eternal. Broken.
Visual Hallucination Reality Leak:
Reality around him begins to show cracks. Sometimes, others see the things he sees. The multiverse bleeds into neighboring timelines, infecting them with mad echoes of "UltSans" as a real being.
A mental virus.
Woven from Determination, trauma, and unresolved grief.