UltSans moved through the cold corridors of the Institute, his footsteps silent against the bloodstained floor. The flickering lights overhead cast long, shifting shadows against the reinforced walls, but he barely noticed.
He felt strange.
Something was… changing.
His breath hitched as he felt a faint tingling sensation crawl through his scalp. He didn't know it, but his hair was lightening, the darkness fading away. The once-muted tones of his golden strands brightened, turning into a glowing, yellow-gold hue, almost shimmering in the darkness.
His eyes followed next.
The deep, murky shade in his pupils vanished, replaced by an intense, almost ethereal blue glow. The dim corridors reflected the light of his new, unnatural radiance.
Then, it happened.
A tear fell.
He froze.
His left hand lifted instinctively, fingers brushing against his damp cheek.
He was… crying.
His sockets widened in disbelief as he stared at the moisture on his fingertips, confusion twisting his expression.
UltSans:"...W-why?... Why am I suddenly crying?..."
His voice wavered, breath hitching in his throat.
UltSans:"I don't feel anything, and yet... My head... It's—it's overwhelmed..."
His fingers curled against his palm as he shook his head, his grip tightening as if trying to ground himself.
UltSans:"I-I don't... I don't regret anything. I-it has... It has to be done..."
His breath trembled.
UltSans:"It has to be done..."
His body shook, a deep shudder rattling through his frame.
UltSans:"No... N-no... I learned. I became the best version of myself. I can't..."
His voice broke.
UltSans:"I can't be myself anymore."
He squeezed his eyes shut, as if trying to block something out.
UltSans:"I have to... I have to..."
But the words wouldn't come.
Something inside him refused.
And that terrified him.
He gritted his teeth, his breathing uneven.
UltSans:"Why can't I? I have to focus... What is done, it's done... And no humans will affect me... Not anymore..."
His voice dropped into a whisper as he forced himself forward, his steps unsteady.
UltSans:"Come on, Sans... You learned to be the best version. Stop hesitating..."
But the weight in his chest didn't leave.
And the tears didn't stop.
Deep within UltSans' subconscious, Abyss returned to the place where it had first encountered Chara, Azzy, and Hatred.
The air was different now.
Hate was gone.
But something still lingered.
The moment Abyss arrived, Chara turned—her crimson eyes widening in pure shock. For a brief second, she almost gasped.
Then—her expression hardened.
Her form flickered, the static haze around her intensifying as she forced herself to regain control.
She exhaled sharply, her stance rigid.
Chara:"What do you want now?"
Abyss hesitated for a moment, then spoke.
Abyss:"Bond."
Chara's face twisted into a scowl.
Chara:"You already know I won't allow you. No matter how you look, no matter how much scarier you try to get, I won't let any amount of hate change who Azzy is."
Abyss remained still.
Then, in its fragmented, broken voice—
Abyss:"Hate… is gone."
Chara's eyes narrowed. Suspicion.
She didn't move, but her entire stance shifted.
Chara:"...Explain. Now."
Abyss:"I absorbed. Evolved. I cleaned. I help. Let me help him too."
A long, heavy silence followed.
Chara didn't answer immediately. She simply stared.
Then, slowly, her gaze drifted to the side—her expression unreadable.
For a moment, she seemed deep in thought.
Then, with a slow, exasperated sigh, she turned back to Abyss.
Her glare softened—but only slightly.
Chara:"...But the instant I see you being a threat, I'll erase you. Clear?"
Abyss didn't hesitate.
Abyss:"Clear."
The deal was made.
Chara's form flickered for a moment—
And then, the bond began.
Abyss felt it before it could even react.
The connection wasn't forced. It wasn't even intentional.
The moment Chara accepted it, the bond happened instantly, as if something far greater, far older, had already decided it before Abyss had even moved.
Abyss was no longer an outsider.
It was now part of this broken soul.
And it would soon see just how deep that fracture ran.
The moment Chara accepted, the bond began instantly—but not by Abyss' own doing.
Something far greater had already decided its fate.
Abyss felt a force latch onto it, something ancient, something immovable. It wasn't a simple connection, not like the bonds it had formed with past hosts. This was fundamental, an inescapable link to existence itself.
It had bonded before—melded with flesh, invaded minds, intertwined with nervous systems.
But this was different.
This wasn't just binding to a host.
This was being chained to something beyond comprehension.
Phase 1: Bonding With the Soul—The Determination Link
The first thing Abyss felt was Determination.
Raw, unyielding, eternal.
It crashed into Abyss like a tidal wave, flooding through every particle of its being. It wasn't a foreign power—it was fundamental. A force that defined existence, that refused to yield to time, space, or even death.
For the first time, Abyss understood why Hate had never controlled UltSans.
Chara had been the one holding the soul, her Determination the dominant force, shielding UltSans from being consumed.
And now, that same Determination was being poured into Abyss.
It wasn't optional.
It wasn't something Abyss could resist or fight.
It was fate.
The soul of UltSans—a soul that had learned True Determination through suffering, through resets, through countless trials—recognized Abyss.
And it chained Abyss to it.
Abyss shuddered, its essence quivering as it felt its entire being being rewritten once again.
Not by Hate.
Not by corruption.
But by something far stronger.
This was not corruption.
This was evolution.
The once unstable, flickering force within Abyss solidified. Its body, its core, its very essence became something new.
It felt the soul's weight.
The chains of Determination wrapped around it, binding it to this eternal existence.
And in return, Abyss gained something it never had before.
Purpose.
Not just survival.
Not just consumption.
It belonged here now.
The red glow emerged from within, pulsing through its veins like molten fire, marking the change—not a physical transformation, but a spiritual one.
It was no longer just a symbiote.
It was now a part of something much greater.
Phase 2: Merging With the Body—A New Host
With the soul's bond forged, the next phase began immediately.
Abyss turned its focus to UltSans' body, and it was immediately met with something it never expected.
This wasn't a normal body.
It wasn't human.
It wasn't monster.
It was a contradiction.
The bones, the organs, the very structure of UltSans' being shouldn't have been alive.
Everything about it was broken, decayed, ruined—yet somehow functioning.
His ribs were fractured, his heart barely beating, his body running on something far more unnatural than biology.
Abyss felt the corruption.
Not from Hate.
But from reality itself rejecting UltSans.
His very existence was unstable, shifting between what was alive and what should have long since perished.
Abyss spread through his veins, reaching into every crevice, every fracture, every fragment of something that should not be.
It didn't just coat UltSans.
It sank into him.
The process was unlike anything Abyss had done before.
Other hosts had resisted, struggled, fought against the intrusion.
But UltSans' body welcomed Abyss.
It pulled Abyss in, as if it had been waiting for something to fill the cracks.
Abyss' red glow spread through UltSans' bones, his marrow, his sinew. Every part of him became one with the symbiote—not as a separate entity, but as a perfect fusion.
Abyss was not an external parasite.
It was now woven into the very fabric of UltSans' being.
This wasn't a host taking on a symbiote.
This was a symbiote becoming a body.
UltSans shivered, his breath hitching as his body adjusted to the presence of Abyss within him.
His heartbeat quickened.
His muscles felt lighter.
His power stabilized.
The flickering, unstable existence he had lived with for so long found something new.
Balance.
Phase 3: Merging With the Mind—A Shared Existence
Abyss had bonded to the soul.
Abyss had merged with the body.
Now, only the mind remained.
It drifted forward, deeper into UltSans' thoughts, feeling every fragment of who he was.
And what it found was a storm.
The moment Abyss touched UltSans' mind, it felt an onslaught of memories.
Pain. Regret. Resets. Betrayals.
Countless deaths. Countless choices.
And above all else—an overwhelming, crushing sense of exhaustion.
Abyss didn't try to control.
It didn't try to suppress.
It simply understood.
For the first time, UltSans was not alone.
Abyss wasn't an invader.
It was an extension of him now.
Abyss saw his resolve. His torment. His struggle.
And it accepted all of it.
UltSans' eyes flickered as the final stage completed.
He exhaled slowly, his body feeling lighter than it had in years.
The burden of his existence was still there—but now, he was no longer carrying it alone.
Abyss' voice echoed softly within him, no longer a separate entity, but a presence within.
For the first time, they spoke as one.
And UltSans took his first step forward—
No longer just a broken anomaly.
But something far, far greater.