There’s a Demon King Inside the Hero

Chapter 1: The Retired Hero and the Former Demon King (1)

“Thank you for enduring the treatment. But… are you okay? You don’t look well.”

“No, it’s nothing…”

After a month of treatment, Kim Suhyeon finished the discharge process and left the hospital.

As he stepped out of the hospital, he looked up at the sky with a hollow gaze.

His cheeks were slightly gaunt, and dark circles had formed under his eyes.

This was because he had been mentally exhausted, tormented by the voice of the Demon King in his head for quite some time.

Yeah, I’m a former hero who saved the world from this so-called Demon King.

Shouldn’t there at least be some sort of reward for me when I returned to my original world?

[You dare act shameless after killing me!]

But all I got was this damn specter constantly speaking in my head.

[A specter? You must have lost your mind.]

Please, shut up…

Because of the constant nagging from the Demon King’s voice, Suhyeon pressed his temples, his head throbbing.

It had been exactly a month since this damn Demon King had settled inside his head.

During the entire month of treatment in the hospital, this guy hadn’t stopped cursing at me even for a moment.

[You’re worth less than dark elf urine!]

[You deserve to be chewed up by a dragon’s teeth!]

[Even a succubus would reject you at night!]

I felt like I’d heard every insult that could possibly exist in the world of Altera.

Two weeks later, he evolved, nitpicking every single thing I did.

When I tried to sleep…

[Aaaaargh!]

I lost count of how many times I was jolted awake by the Demon King’s screaming in my head.

When I ate…

[Did you know that snail-type monsters eat each other’s waste before mating? Ah, the way you’re eating resembles that, with the spoon in your mouth.]

“Ugh!”

When I looked in the mirror…

[The mirror might crack. Even an ogre or a goblin has a better face than that.]

When I went to the bathroom…

[Ha! What’s with that size? Even a gnome’s would be bigger than yours.]

That one was too much, and I banged my head against the wall.

And yet, this bastard.

It became clear as he spoke that the Demon King somehow had knowledge of everything about this world, despite never having been taught.

‘How do you know all this?’

[It seems like all the information in your brain is being shared with me. Whatever you see, feel, or eat, I experience it too.]

A malicious laugh echoed in my mind.

[It’s interesting, really. Like that time in high school when you said, ‘This is it,’ and confessed to a girl, only to get rejected in the most embarrassing way…]

‘Aaaaagh!’

This is a curse. It’s really a curse.

It seemed even the Demon King himself hadn’t expected his curse to manifest in this way, but at this rate, I’m going to die from the stress before I live out my natural life.

I tried humming the calming tune that the elves had taught me for mental peace, but it was useless.

Why is this happening to me…

The only reason I survived adapting to this damn Demon King’s voice was because I spent the entire month focused solely on treatment in the hospital.

Some people came to visit me, either occasionally or in groups, but to Suhyeon, they were all people he hadn’t seen for over a hundred years.

A few familiar faces triggered memories, but that was the extent of it. The genuine feeling of reunion was missing from his heart.

The fact that most of his experiences in this world had faded from his memory became all the more real.

A bitter smile tugged at his lips.

Moreover…

He opened his palm, trying to focus his energy and summon any trace of magic.

…

But it was no use.

In this returned body, there wasn’t even a hint of magic.

The Holy Sword he used in Altera, his superior physical abilities, his exceptional aptitude for magic.

They were all gone.

“Haa…”

At this rate, his aspirations of becoming a hunter and protecting the world were nothing more than an empty dream.

He had been a college student before all this.

But he had long since forgotten all the knowledge from his major, having spent so many years in the other world.

…What should I do?

[Protect the world? How old are you again, thinking like a middle schooler… you sound as foolish as a kobold.]

‘This bastard…’

He knows everything but still speaks so nonchalantly.

Although he kept retorting, it was actually less frequent now.

Even the Demon King seemed to have tired of talking after a month. From the third week onward, he gradually quieted down, only speaking up now and then to pick a fight.

Even though Suhyeon had killed him, a month was a long time.

Talking non-stop for that period was bound to wear anyone out.

Suhyeon considered going home to rest, but…

Come to think of it, where exactly is my house? A hundred years have passed, so it’s understandable that I forgot… but where was it, really?

He considered calling someone to ask but felt too awkward to do so.

Instead, he decided to walk around the city, familiarizing himself with the geography in hopes of jogging his memory.

If that didn’t work, he’d resort to calling someone, anyone.

The place where he had just left the hospital was a busy city intersection.

On the electronic billboard of a nearby building, the news was playing.

A specialist and a news anchor were in the frame.

『Today, we have a specialist who has published a paper on the relationship between monsters and the world. Let me ask right away: what are your thoughts on the Great Cataclysm that occurred 40 years ago?』

The world has changed a lot since then.

From the perspective of this world, it was 40 years ago…

Across the world, mysterious sinkholes, collectively called “dungeons,” began appearing.

And not just a few, but thousands.

Monsters emerged from these dungeons, slaughtering people, and nations united, using every available resource to eradicate these so-called dungeons within their borders.

Humans fought fiercely, but it wasn’t enough to stop the endless hordes of monsters, leading to significant casualties.

However, one year later, a miracle occurred.

A very small number of people worldwide, primarily children under the age of fifteen, either naturally or suddenly awakened as “superhumans.”

These children possessed physical abilities that surpassed human limits, as well as supernatural powers known as “skills.”

With these superhumans leading the way, humanity finally began fighting monsters on even terms. The hunters who hunted these monsters were soon classified into ranks based on their strength.

From 1-star to 7-star.

Currently, there’s an efficient training curriculum for hunters, and those who have awakened their abilities are granted the right to take the entrance exam for hunter training schools between the ages of 10 and 15.

Upon passing, they undergo a four to six-year education before receiving their hunter certification.

Once certified, a hunter is automatically affiliated with the “Union” and receives missions from the organization.

In summary… they’re the ones who carry out missions assigned by the Union.

Most of these missions are dungeon-clearing operations, but not exclusively.

Under the Union’s command, hunters coordinate with one another to clear dungeons efficiently.

While military weapons are somewhat effective against monsters, dungeons in remote areas are often destroyed by long-range missiles and bombers.

However, higher-level dungeons remained intact even after bombardments, and in densely populated areas, such firepower couldn’t be used freely.

Thus, the profession of “hunter,” who directly enters dungeons to eliminate monsters, was born.

[So, such events occurred in this world… Many must have died. Not that it concerns me.]

Hearing the Demon King’s indifferent reaction to such a horrifying event made Suhyeon frown.

‘You speak as if it’s none of your business. Weren’t you once human too, according to what I heard in Altera? Don’t you feel even a bit sorry for the people?’

Though it was hard to believe, the Demon King residing in Suhyeon’s head had once been human.

According to the people of Altera, the Demon King was originally a mage who had used forbidden magic, which deformed his body into its monstrous form.

In short, he wasn’t a god or anything, just a person.

He was merely called the Demon King because people had started referring to him as such.

As a human, he had limitless mana and was recognized for his extraordinary talent in magic application.

However, this promising mage’s pursuit of power led him down a dark path, ultimately becoming the Demon King.

It was said that at the age of 20, he could have become the representative of the prestigious “Tower of Mages,” the dream workplace for mages in Altera, but who cares?

In the end, he was just a thug who lost control of his power.

[What did you say? Do you dare insult me after I’ve remained silent all this time?!]

Ignoring him.

[Tch, you insignificant gnome-sized fool.]

Great, now he’s mixing fantasy insults with curses from this world.

Just as Suhyeon was about to respond with a snarky thought—

[Hmm?]

At nearly the same moment, a blaring siren echoed through the city.

Beeeep!

『This is a real emergency! Displacement energy is increasing at Jeonnam-dong intersection! Citizens are advised to evacuate the area immediately. I repeat…』

The people around began murmuring before quickly breaking into a run.

Displacement energy—the distinctive energy wave emitted when a dungeon is about to form.

Due to its unique nature, sensors capable of detecting these waves were installed throughout the world, allowing authorities to alert citizens swiftly.

When a dungeon forms, the displacement energy gradually increases, and once it surpasses a certain threshold, the dungeon is created.

There’s typically a one to two-hour window before the dungeon forms, enough time for people to evacuate safely.

Knowing this, the citizens quickened their pace to leave the area.

It had been 40 years since monsters first appeared. People had been educated on how to handle these situations, so this wasn’t all that surprising.

However—

[You need to get out of here!]

The Demon King’s voice urgently rang in Suhyeon’s mind.

[It seems that displacement energy can measure the mana of the Demon Realm. I can feel the mana from the Demon Realm in the atmosphere. Run! The mana is increasing too quickly!]

“What…?”

Cold sweat dripped down Suhyeon’s back.

Though rare, there were instances when displacement energy increased rapidly instead of gradually.

In those cases, every time without fail, a monster would be “summoned by surprise” without warning.

Suhyeon reacted instinctively.

He glanced around, searching for anything he could use as a weapon.

His eyes landed on a broom placed by the entrance of a restaurant.

Alright, this will do.

Crack!

Just as he grabbed the broom, the sound of an egg cracking came from above.

A magic circle, just large enough for a person to stretch out their arms, appeared in the sky, and something dropped from the crack in the air.

Sliiick.

It was a frog-like monster with a long, flickering tongue.

In Altera, it was called a “Totnoll.” Here, it was known as a “Living Tongue,” an F-rank monster.

The monster appeared before the panicked citizens.

“Kyaaaaah!”

“Run!”

“Why is the monster already here?!”

As citizens screamed and fled in the opposite direction of the monster—

[Hey! What are you doing?!]

‘I need to save these people.’

Suhyeon’s response was calm but filled with resolve.

Gripping the broom like a sword, he moved toward the Living Tongue, heading in the opposite direction of the fleeing citizens.

‘When a monster is summoned by surprise, hunters aren’t always able to respond quickly. At least, I can try to hold it off.’

[What are you, insane? You don’t have any power! No magic, no superior physical ability!]

‘Have you forgotten, Demon King? I defeated you and saved an entire world.’

Though nervous, Suhyeon swallowed hard and pretended to be calm.

‘Do you think a hero who saved a world would cower before some low-level monster?’

[You damn middle school syndrome brat!]