Author's Note: This story is just a foundation for a larger one I'm planning about a transmigrant in the world of Adventure Time, specifically in Fern. If you like it and it gets support, I'll continue it. The goal is to reach 15 stars to see if there's interest. Thanks for reading—take care, and see you in the next adventure!
Let's continue:
Life always arrives when you least expect it. One moment you don't exist—you are nothing—and the next, without any warning, you're alive. There are no instructions, no clear explanation of how you got there. It just happens. Then instinct takes over and pushes you forward: live, adapt, move, endure. If you're human, you develop knowledge, doubts, questions. If you're an animal, you survive on instinct and the most basic reasoning.
I was human.
A human who, from the moment I became aware of my own consciousness, began to feel a void that's hard to describe. It wasn't sadness, nor ambition. It was a constant, quiet desire—something I couldn't name but that was always there, watching me from the back of my mind. Over time, I realized I didn't want to keep being who I was, so I decided to become someone else.
I chose to become a soldier.
It wasn't an impulsive decision. I prepared, trained, and followed through. I'm proud of it, because I protected what I called my homeland at the time. I didn't have a family—not because I couldn't, but because it was never a priority. My life was focused on something else. There were relationships, a few partners here and there, but nothing serious, nothing that took root. Everything was temporary—even me.
Do I regret that now?
The answer is simple, almost automatic.
"No, I don't regret it."
And yet, at this point, the question carries no real weight. In the end… what does it matter now?
The last thing I saw before I died was a sign. A simple advertisement, nothing special to the world—but to me, it was everything. On it was my favorite character.
"Kenjaku."
I didn't feel fear. Nor anxiety. What I felt was calm. A strange, deep calm, as if something inside me had finally let go of a tension I'd been carrying my entire life. I felt light. Free. Complete in a way I had never experienced. Because of that, I spent a few moments happily dead, with my entire life reduced to distant, detached memories—almost unreal.
Then something else happened.
I felt a pull.
It wasn't painful or violent. There was no panic. I suppose it was normal—after all, it was my first time dying. Still, suddenly everything filled with light. A white light, overwhelming, impossible to ignore. I blinked—a simple, everyday action I hadn't felt since I was alive.
And then it happened.
I felt.
I felt my body.
I slowly looked around, trying to understand where I was. The place had nothing to do with what I remembered. Everything was in ruins. Broken structures, remnants of what must have once been inhabited, and a heavy sense of abandonment hanging in the air. I didn't know how I had ended up there, but I was struck by how deteriorated everything was, as if the world had been left to rot.
I looked down at my hands out of instinct.
And froze.
These weren't the hands I remembered. They were thinner, smaller—clearly feminine. The skin was different. The shape, too. For a moment, I thought my mind was playing tricks on me, but the sensation was too real.
This wasn't normal.
None of this was.
Before I could process it fully, something appeared in front of me.
A floating screen.
It didn't look like traditional magic or known technology. It was simply there, suspended in the air, as if it had always belonged.
"Immortality Template."
Below it, a percentage began to rise.
"1%...5%...50%...99%...100%..."
When it finished, new words appeared.
"Welcome to the template system of the last thing you saw."
For a second, I thought I misunderstood.
"You can obtain a wall template, an air template, or even the sky. However, for your fortune—or your misfortune—the last thing you saw, my dear host, was the character Kenjaku."
A chill ran down my spine.
"A practically immortal being. And that is what you will now be: an immortal in a post-apocalyptic world."
The screen didn't stop, as if it enjoyed explaining my situation.
"You may be wondering what world you are in. Do you think you are in Jujutsu Kaisen? You are mistaken, dear host. You are in Adventure Time. A world even more dangerous, chaotic, and unpredictable."
Each word felt heavier than the last.
"To help you keep up, one of the advantages of this template is eternal youth."
A brief, almost mocking pause.
"The downside? Your base form will be female."
My eyes widened as everything started to make sense.
"To access the other identities Kenjaku has possessed, you must train. But don't worry—you'll have plenty of time, dear host."
The screen continued.
"You are currently in the world of vampires, where Marceline hunts them. I hope this information helps."
That explained the ruins.
The atmosphere.
The constant sense of danger.
"The template grants you excellent aptitude for sorcery and accelerated learning, without falling into the madness typical of the Adventure Time world. You will also have partial access to Kenjaku's memories."
The final message appeared slowly.
"Good luck."
The screen faded, dissolving into the air as if it had never existed. I remained still, my mind blank, heart racing, with one certainty settling deep inside me.
My death hadn't been the end.
It had only been the beginning.
I stood there, expressionless, as I finished examining myself. There wasn't much room for denial. They were right. I had transmigrated—if that was even the correct word for it.
I looked at my body more carefully.
And then I recognized it.
A female body.
More than that… I knew exactly whose it was.
Kaori Itadori.
Nothing out of the ordinary within the absurd. I could deal with it. It was uncomfortable, sure, but not impossible. At least my mind was still mine, even if the idea of fully adapting to this body came with concerns I chose not to dwell on too much—for now.
Suddenly, a sharp pain pierced my head.
It wasn't a normal physical pain. It went deeper—like my mind was being forcefully reorganized. Fragments of memories began to pour into me, one after another, but not chaotically. It was as if something was filtering them, making sure they wouldn't affect my personality too much.
Even so…
They were heavy.
Eventually, the memories settled.
And then—
Silence.
I stared into nothingness for a long time, not thinking about anything in particular. Just… existing.
"…So I really am here," I thought, now observing my surroundings more carefully.
Now I could see it more clearly. Nature had reclaimed most of the place. Plants growing through ruins, structures worn down by time. It was a post-apocalyptic world, without a doubt.
Strangely…
It didn't feel unfamiliar.
There were positives.
I knew how to use Kaori's technique—or rather, the technique that was now mine as well. That was a major advantage. And beyond that, I could feel it clearly.
There was more energy flowing through my body.
Not normal energy.
To avoid confusion, it was better to call it what it was.
Cursed energy.
I also understood something else.
This body hadn't appeared out of nowhere.
It had died during the nuclear war.
Before I arrived, it was nothing more than a deteriorated shell, a body ravaged by radiation, barely alive. The template had repaired it, reconstructed it, given it a functional form.
The form I now had.
I looked at my hands again.
But this time…
They didn't feel foreign.
I already knew I felt empty before, but this…
This was something else entirely.
"Isn't this a bit excessive?" I thought, my gaze unfocused.
At least there was something comforting about all of this.
I hadn't left anyone behind.
No one waiting for me.
No attachments.
That made it easier to move forward.
I stood up slowly, testing the balance of this body. Getting used to its weight, its structure, the way it moved.
I was naked.
Something I'd need to fix soon.
Not out of embarrassment.
Just practicality.
I began walking, searching for anything I could use to cover myself.
As I moved, vague memories of Adventure Time surfaced. Fragments, incomplete scenes—but enough to establish priorities.
First.
The Enchiridion.
Second.
Increase my magical power. My reserves. My control.
Everything.
And third—
The most important.
Survive.
I walked for several minutes through the ruins, moving without a clear destination while observing what remained of what had once been a populated place. Collapsed structures, split streets, buildings consumed by time.
At the same time, I paid attention to something more important.
Energy.
I could feel it in my surroundings with unsettling clarity. It was similar to sensing ki, but not the same. This energy was heavier, denser.
I could detect presences filled with negativity from a distance.
Even without seeing them.
That was an advantage.
If something hostile approached…
I'd know.
But there was also a downside.
If there were still humans around, they probably wouldn't emit that kind of negative energy.
Meaning I could mistake them for the environment.
And considering how I looked right now…
I wasn't exactly approachable.
As I walked, I stepped on something soft.
I moved my foot slightly and looked down.
A rag.
Dirty. Worn. Full of holes.
But still usable.
Better than nothing.
I picked it up and wrapped it around myself as best as I could. Not elegant, but functional.
Good enough.
I kept walking.
After a while, I noticed something interesting.
I wasn't getting tired.
No strain in my legs. No shortness of breath.
Maybe eternal youth had something to do with it.
If so…
At least I wouldn't die from something as basic as exhaustion.
Though, of course…
If someone cut off my head, that would be a different story.
As I kept moving—
Something changed.
I felt movement.
Many life forms approaching.
All of them carried the same signature.
Pure negativity.
Dense.
Distorted.
Not just one.
A group.
Without hesitation, I moved quickly and slipped into a partially destroyed building, hiding among shadows and debris.
Watching.
Waiting.
And when I finally saw them…
I understood.
Mutants.
But not like the ones I vaguely remembered.
This was different.
Humans twisted beyond recognition.
Cows distorted into unnatural shapes.
Elephants fused with other creatures.
Bodies combined in grotesque, impossible ways.
There were too many.
And each one worse than the last.
"…That explains it," I muttered quietly.
Now I understood why the series only showed certain types of mutants.
This…
was too much.
They ran into each other.
Attacked.
Destroyed one another without order.
Some literally absorbed others, merging into even more horrifying forms.
Growing.
Changing.
Becoming worse.
"Is that… a giraffe?" I thought, focusing on one creature.
It had no head.
Its body was full of irregular holes, as if something had burst through it from the inside.
Seven legs.
All different sizes.
Its movement…
unnatural.
Someone inexperienced would've frozen in fear.
I didn't.
I had seen worse.
Curses.
Abominations.
Beings born from hatred.
But one thought did bother me.
If this alone was dangerous…
What would happen if someone controlled them?
The idea alone made me stay perfectly still.
This world wasn't just broken.
It could get much worse.
After nearly three full hours, the creatures finally left the area. Silence slowly returned—heavy, uneasy—like the world itself was holding its breath.
Once I was sure there was no trace of them left, I stepped out of my hiding spot and walked carefully, watching the direction they had gone.
I studied the terrain.
If there was one thing movies—and my own instincts—had taught me, it was this: when a group moves with that much urgency, it's not random.
They're heading toward food.
I turned my gaze in the opposite direction—from where they had come.
They had already eaten there.
I swallowed.
Almost out of habit, I made a small prayer. I didn't know if it would do anything. In this world, there were too many hells, too many layers—maybe fifty or more.
Right now…
I didn't care which one listened.
I looked back toward the direction they had gone.
"If I go now and get there first… I might be able to warn the human survivors," I thought. It might not change much—but even a small advantage could make a difference.
I didn't consider myself evil.
But I wasn't good either.
I simply refused to let boredom dictate my existence.
If I was going to be eternal…
I might as well do something.
Help people—so long as they didn't provoke me.
And if I had to kill…
I would.
It wouldn't be the first time.
In my previous life, as a soldier, I learned to adapt quickly. I had taken lives before—people who posed direct threats. It wasn't something I was proud of, but it didn't haunt me either.
It simply happened.
And if I added Kenjaku's partial memories…
The number didn't matter.
It wasn't worth counting.
So I let it go.
I looked up at the gray, silent sky.
"Guess it's me against the world," I thought, the rag around my body swaying lightly in the wind.
I stood there for a full minute.
Still.
Accepting it.
"…Whatever," I thought finally.
And I started walking, following the trail the mutants had left behind, my mind already forming plans with unsettling calm.
Plans belonging to the one who, from now on…
would be known as Kenjaku.
The first—
Stay close to humans.
Not out of altruism, but to avoid the madness that comes with total isolation. Even minimal interaction mattered.
The second—
Try to establish some kind of connection with Marceline.
It could be useful.
For both of us.
An immortal companion in a broken world wasn't a bad idea.
And the third—
The most important.
Find Simon Petrikov.
If anyone had the Enchiridion…
It was him.
Those were my basic plans.
Nothing grand.
Nothing final.
Just the first steps…
of a life that had just begun.
Again.
"Let's see…" I thought, adjusting my energy the way the memories indicated.
I wasn't trying anything complex.
I didn't need to show power.
I just needed to adapt.
Movement.
Control.
Understanding.
The basics.
I let the energy flow through my body.
Carefully.
Then I activated the cursed technique—anti-gravity.
Immediately, I felt the shift.
My weight changed.
I didn't remove it completely.
I wasn't reckless.
The goal wasn't to nullify gravity—
just to manipulate it.
Reduce it enough to increase speed.
To understand it.
With a small burst of energy, I jumped.
Up.
Into the sky.
From there, everything became clear.
Nature had taken over.
Trees.
Vegetation growing wildly.
Ruins being swallowed by green.
Ooo was rebuilding itself.
In its own way.
As I fell, I redirected energy to my eyes.
Time to try something more precise.
Using Kenjaku's knowledge—and how easily I had absorbed it—I formed a binding vow.
Carefully.
Words mattered.
Every condition mattered.
"Binding vow. For the next twenty seconds, my vision will calculate the distance, route, and arrival time of the beasts I observed earlier. In exchange, I will give up five percent of my total energy for today, which cannot be recovered until midnight."
The vow activated.
Information flooded in.
Clear.
Precise.
First—
The destination.
The nearest human settlement.
Or what was left of it.
Three hundred kilometers away.
On foot, days.
But that didn't matter.
The mutants moved fast.
Close to vehicle speed.
Some even faster.
That reduced the window to days.
The calculation finished.
I landed.
Set my direction.
And started running.
Not at full speed.
No need.
This wasn't a race.
Not yet.
This was adaptation.
Each step.
Each adjustment.
Each flow of energy—
an investment.
Because in this world…
You don't get a second chance for mistakes.
Only one.
And it's final.
So no.
I didn't plan on making one.
After a while, I noticed something.
I needed something basic.
Clothes.
And luckily…
I found them.
A small camp.
Improvised.
Poorly organized.
Abandoned.
Not peacefully.
Signs of attack everywhere.
Still—
Surprisingly intact.
Probably vampires.
Not something worse.
I searched quickly.
Found a backpack.
Clothes inside.
Worn.
But usable.
I dressed.
Simple.
Nothing flashy.
Functional.
Food.
Didn't need it now.
But later—
yes.
Also…
it helps.
Reminds you you're still human.
Sort of.
Basic supplies.
Useful.
Everything matters.
Then I saw it.
A spear.
And a wooden stake.
I hesitated.
Then took the spear.
Better reach.
Better utility.
As soon as I held it, I instinctively infused it with cursed energy.
Not too much.
Just enough.
No point overdoing it.
At best…
third-grade.
Maybe not even that.
So I reinforced it.
Durability.
Stability.
Reliability.
That was enough.
I stored the stake.
Adjusted the backpack.
Took one last look.
Nothing else worth taking.
So I left.
And kept running.
Stronger.
More adapted.
More prepared.
Because improvising works.
But planning?
Planning is better.
I closed my eyes for a moment, letting Kenjaku's memories flow freely.
That's when I noticed it.
It was night.
And if it was night…
then vampires weren't just possible.
They were here.
I felt it.
A presence.
Following me.
Not clumsy.
Not rushed.
Patient.
Experienced.
Testing me.
I stopped.
Didn't speak.
Didn't move abruptly.
I simply turned slowly.
Looked exactly where I knew it was.
Letting it know—
I was aware.
Silence.
Then movement.
Circling me.
A voice.
"Well, well… a human out here?"
Mocking.
Amused.
I said nothing.
Just watched.
Tracked.
It noticed.
Paused.
But didn't come out.
Still playing.
"Humans used to travel in groups. Now what? You think you're something special just because you can run that fast?"
Arrogant.
"If our king were here, you'd be nothing."
Still hiding.
I exhaled slowly.
"What do you want?" I asked calmly.
Silence.
Then—
"So that scar on your forehead… did one of us leave you a warning?"
Laughter.
I looked at him.
Unmoved.
"No."
Pause.
"I just put my brain into this body."
Not entirely a lie.
Not the full truth either.
Silence.
Then—
"You've got a sense of humor."
His tone shifted.
"I'm one of the talented ones. I serve the Empress directly. Top ten."
Not a threat.
A statement.
"…And?" I asked.
He stepped closer.
"Your blood is interesting."
Curiosity.
"Not quite human."
He moved behind me.
Didn't attack.
Waiting.
"And if I'm not?" I replied.
Tension.
Instant.
"Then I'll have to kill you."
He attacked.
Fast.
I moved instantly.
Dodged.
Rolled.
Countered with a kick.
Solid hit.
He stepped back.
Felt it.
But didn't care.
"You think that'll stop me?"
I stayed silent.
Analyzing.
I could kill him.
Easily.
But that wasn't the goal.
I wanted to learn.
Test limits.
Adapt.
So I smiled.
And stepped forward.
This fight—
wasn't about survival.
It was about learning.
The vampire lunged with brutal speed, a dark blur slicing through the night air—but my body reacted before my mind fully caught up. I shifted to the side, feeling the rush of wind where my neck had been a second ago.
I immediately channeled energy through my body, reinforcing everything—muscles, bones… and just in case, my neck as well. I had no intention of testing how sharp his fangs really were.
The vampire stopped and slowly turned his head, his expression twisted—almost fascinated, like he had just found a new toy.
"Interesting…" he muttered, licking his lips with an unnatural tongue, his fangs fully visible. "Very interesting."
His gaze scanned me from head to toe.
"You'll make an excellent dessert for my queen… maybe I'll even earn a kiss."
…
…
…
I stayed silent.
First, because what the hell did he just say.
Second, because I wanted to test something.
I wanted to see how far I could push this body—its techniques, its magic, everything Kenjaku knew.
Then—
His presence distorted.
Gone.
Invisible.
My eyes sharpened, but I didn't panic. It caught me off guard—but not enough. His presence was still there, like pressure in the air.
The first attack came from behind.
I leaned just in time.
Then another.
And another.
We moved fast—jumping through trees, crossing ruins, cutting through broken paths like a game of predator and prey.
I dodged.
Turned.
Adapted.
Learning his rhythm.
After a while, the environment shifted.
The ground grew damp.
The air colder.
I stopped.
A lake stretched out before us.
Dark.
Still.
Too still.
"Well," the vampire said, appearing a few meters away, "you've got good awareness."
I glanced around at the wooden bridges crossing the lake.
Then said, calmly:
"You smell like shit."
The vampire frowned—three clear lines forming on his forehead—but quickly shook it off, regaining his twisted smile.
"Now I'm sure you're not human… but you still are," he said, genuinely intrigued. "That makes your blood even more interesting."
"Just my blood?" I replied, feeling the familiar weight of my backpack.
I reached in and pulled out the spear.
Spun it lightly.
Balanced.
"Going to attack?" he grinned. "I like it when prey fights back."
"So do I," I answered, pointing it at him.
"Come at me."
I moved first.
No hesitation.
The clash was immediate.
The spear cut through the air, but he slipped past it like a shadow, countering with a claw strike aimed at my chest.
I blocked.
Felt the vibration through my arms.
Strong.
Stronger than expected.
I pivoted.
Swept his legs.
Forced him back.
Planted the spear.
Used it to launch myself—
And kicked him straight in the face.
The impact sent him sliding across the wet ground.
He laughed.
Actually laughed.
"This is fun!"
Then—
Gone again.
This time, I closed my eyes.
Felt the air.
The pressure.
The shift behind me.
I turned—
And struck.
The spear grazed his shoulder.
A growl.
"Found you."
He clicked his tongue and stepped back, now more serious.
"Definitely not normal prey."
I smiled slightly.
"And you're not the first one who's tried to eat me."
Not a lie.
Memories flickered.
Kaori's body.
Men who thought they could take advantage.
Every single one of them…
dead.
Brutally.
No trace left.
The thought passed.
And then—
We moved again.
This time, he wasn't playing.
No more games.
Every attack was meant to kill.
Direct.
Efficient.
Lethal.
And right before he could land a decisive blow—
I spoke.
"I got what I wanted."
My voice was calm.
Too close.
Right next to his ear.
He froze.
For a fraction of a second.
Enough.
A blade of cursed energy pierced through his back.
Clean.
Precise.
His presence destabilized instantly.
The air around him trembled.
He tried to escape.
To disperse.
To vanish.
I didn't let him.
I raised my hand.
Binding vow.
No hesitation.
"I will create barriers to contain entities like this. These barriers will be weak on the inside, but extremely durable from the outside. They will only contain the essence of the vampire that is captured. Entry and exit are allowed—except for the one trapped inside."
The words sealed.
The pact formed.
His essence was ripped from his body—
and trapped.
Frozen.
Suspended.
He couldn't move.
Couldn't escape.
Couldn't even scream.
I observed the result.
Calm.
Emotionless.
"…Since I'm strong enough, I don't need to make an ugly vow," I thought, turning away.
The lake returned to silence.
The night stabilized.
Like nothing had happened.
I looked ahead.
Toward my path.
"Time to enter society."
And without looking back—
I started walking.
End of Chapter 1.