Park Cheol-woo took out a laptop. It was large, thick, and heavy, but instead, it was sturdy enough to pass military specifications. This laptop wouldn’t break even if thrown on the ground. In emergencies, it could even be used as a shield.

However, this laptop weighed over 5kg.

Seo Jung-woo looked at it and thought of a laptop he had seen while browsing the internet in the other world.

‘That one only weighed 1kg. Plus, it was thin and light.’

But he couldn’t bring a laptop from that world into this kind of battlefield.

‘It would probably break within a few days or get fried by electromagnetic interference.’

The characteristic window logo that appeared when Windows started up popped up on Park Cheol-woo’s laptop screen.

‘In our world, Windows is still XP, but over there, it’s already up to version 10. How long will it take for this world to go from 1 to 10?’

Windows XP was released after the monsters invaded. He was a little surprised to find out that the other world also had XP. However, XP had been released much later in this world.

Several minutes after turning on the laptop, the Windows desktop finally appeared. Park Cheol-woo used a photo of his wife and two daughters as his wallpaper.

Park Cheol-woo’s family had gone missing because of the monsters. In this world, being missing was worse than being dead. Missing meant that even a body hadn’t been found.

Park Cheol-woo launched a music program and loaded the rearranged sheet music for If We Could Meet Again.

“A four-member girl group sang this before, but they messed with it too much while trying to arrange it themselves, and the song got ruined. This is the arrangement I made to fit their voices back then. Of course, I never gave it to them.”

As he tweaked the score here and there, he explained,

“I’ll reassign parts to better suit the amateurs you’re working with, adjust the arrangement a bit, and rearrange the instruments. This is going to take some time.”

“Can you finish it today?”

“Of course. About three hours. I should also give them proper advice. These amateurs have good voices, so if they understand my advice properly, they should at least be able to outdo the four-member group.”

“Write down the advice. In detail.”

Thinking of Seo Sora from the other world, Seo Jung-woo added,

“So even an idiot can understand it.”

“No need to bring civilians into this battlefield. Got it.”

Park Cheol-woo started working. He reconfigured the virtual instruments, reassigned each part, and wrote down the important points—where to focus, bad habits to fix, and things to be careful about.

Seo Jung-woo passed the time responding to Park Cheol-woo’s occasional remarks as he worked.

Three hours later, Park Cheol-woo hit the save button with confidence.

“This won’t be a hit, but at least they won’t embarrass themselves.”

“Thanks.”

Park Cheol-woo held out a USB memory stick.

“No need to thank me. This is just repayment for saving me earlier.”

Seo Jung-woo took the USB and joked,

“What about the times I saved you before?”

“Put it on my tab. I’ll return the favor someday.”

“I’ve heard that before.”

“Keep adding it to the tab.”

Seo Jung-woo slipped the memory stick with the sheet music files into his pocket.

Though it was just a revision of a song that had already been arranged for four voices, adjusting it to suit the singers and providing detailed advice in the middle of a battlefield was no easy task.

‘This guy should be doing music.’

He knew Park Cheol-woo was talented, but he couldn’t easily tell him to go back to being a composer. He knew that Park Cheol-woo became a hunter to take revenge for his family.

Seo Jung-woo stood up, unzipped his bag, and pulled out a glass jar. He tossed it to Park Cheol-woo.

“Try this too.”

Park Cheol-woo caught it with one hand. When he saw the dark brown granules inside, his eyes widened slightly.

“Huh? Is this... real coffee?”

It wasn’t ground coffee beans for brewing but freeze-dried instant coffee. This type of coffee was usually mixed with sugar and dissolved in water.

Brewed coffee made from coffee beans was outrageously expensive, and freeze-dried coffee wasn’t much different.

In this world, most coffee was synthetic instant coffee made with added flavoring. That was what people usually drank on the battlefield.

Seo Jung-woo also pulled out a jar of sugar.

“Two scoops of coffee, two scoops of sugar. That’s how they drank it in the 20th century, right?”

“Real sugar too?”

In this world, sweetness came from saccharin.

Technically, coffee and sugar were available for purchase here too. It was just that they were ridiculously expensive. Real coffee and sugar were luxuries.

Park Cheol-woo gave him a sincere warning.

“If you keep wasting money like this, you’ll end up like me.”

“Just drink it.”

Park Cheol-woo looked at the coffee and sugar, then smirked.

“This job must be making you a lot of money. Got it. I’ll drink it sparingly.”

“Don’t hold back, go ahead and enjoy it. I’ll bring more next time I come.”

“Really? Then I’ll drink it without hesitation.”

“Ah, is there anything else you want?”

“Hmm... Chocolate? Or is that too expensive?”

“Okay. Next time, chocolate.”

Seo Jung-woo slung his bag over his shoulder. Just before stepping out of Park Cheol-woo’s small personal tent, he asked, just in case,

“By the way, this song... It wasn’t made in the 20th century, was it?”

If it was, then the same sheet music should exist in the other world.

“20th century? Back then, I didn’t even know what composing was. If the world hadn’t turned into this mess, I wouldn’t have touched music at all. My real hobby was gaming. I used to be a Starcraft ranker.”

“Got it. That’s enough.”

Seo Jung-woo left the Jeokseong Gate defense line in northern Gyeonggi Province and returned to Seoul. He took a bus on the way back. The bus roof had designated spots for shooting. If a monster appeared, passengers were expected to climb up and open fire.

On the opposite lane, he saw an army truck heading toward the defense line. Armed soldiers were seated inside the truck.

Seo Jung-woo gave them a casual salute.

“May luck protect you.”

He returned home.

Seo Sora wasn’t there. Since his safety had been confirmed, she had to focus on her own work.

“She said she had a reconnaissance mission. Guess she’s not back yet.”

Seo Sora was a sniper with a long-range surveillance skill. That skill had various uses, but it was particularly useful for reconnaissance missions.

For important facilities, relying solely on surveillance sensors wasn’t enough. The moment a gate opened nearby, sensors were usually the first to go offline.

That’s why, when security needed to be reinforced, hunters with surveillance skills like hers were hired to guard the area.

Seo Sora was highly sought after because she was capable of both surveillance and combat.

Seo Jung-woo turned on his computer.

“I never noticed before, but it’s slow.”

Compared to computers in the other world, even the boot-up speed was sluggish.

There was internet in this world too.

However, fiber-optic cables weren’t installed in homes because the cost of maintenance due to monsters was too high. Instead, people relied on wireless networks.

He opened a web browser.

“The internet is slower than the other side’s too. Once you’ve used good things, the difference becomes painfully obvious.”

He searched for a composing program online. He found the same one that Park Cheol-woo had used, bought it, and downloaded the installation file. The slow internet connection made the process take quite a while.

Once the installation was finally complete, he opened the sheet music that Park Cheol-woo had given him. Notes left by Park Cheol-woo were displayed in sticky-note form throughout the sheet.

“I need to print this…”

There was no working printer in his home.

He used to have one, but last year, a gate had opened nearby, causing all his electronics to break.

Since he needed his TV and computer immediately, he had them repaired, but a printer wasn’t essential, so he left it as it was.

“Should I bring back a printer from the other world too? They’re cheap there.”

In this world, household electronics were generally expensive. Instead, they were designed so that only the burnt-out parts could be replaced for repairs.

“I wonder if this program would run in the other world.”

He opened the save options and stored the sheet music in an older file format.

The next day, Seo Jung-woo crossed into the parallel dimension once again.

He returned to the exact same moment he had left. Since there had been no one at home when he crossed over, the house was still empty when he returned.

He turned on his computer. Unlike the other world’s machine, this one displayed the desktop within seconds.

“Let’s see…”

He searched for the same composing software on a digital marketplace.

It was there. However, the version was more advanced than the one in the other world.

Since it wasn’t a professional studio program but a personal-use software, the price wasn’t too high.

He paid with his credit card. A wallet he had found recently had a credit card inside.

After completing the installation, he opened the sheet music file from the other world.

The latest file format wouldn’t open. An error message popped up.

“I knew it.”

He had also brought a version saved in an older file format from the other world.

He opened that file.

The sheet music displayed correctly on the screen. The notes were intact as well.

“It works! The old file format opens just fine.”

He re-saved the sheet music in the latest format, then composed an email.

ES Entertainment’s president, Oh Dong-cheol, heard the notification sound and pulled out his smartphone.

“An email…? Dimension sent an email!”

Seo Sora, Yoon Nana, and the twins, Park Ha-yeon and Park Da-yeon, all turned their heads sharply.

Dimension was the stage name created by Seo Jung-woo.

Yoon Nana hurriedly asked,

“What did he say about our song? Did he say it wasn’t bad?”

“Nana, if you have any conscience, you shouldn’t be asking if it’s ‘not bad.’ You guys still have a long way to go.”

“I know that! So, did he say he could help us?”

“I haven’t even opened the email yet.”

Oh Dong-cheol opened the email on his smartphone.

For the four eager faces watching him, he read the contents aloud.

“He listened to all the song files you sent. He acknowledges your effort, but if you keep singing like that, you’ll crash and burn at light speed... Oh. He’s pretty blunt, huh? Ha, hahaha.”

Yoon Nana’s shoulders slumped.

“I guess he didn’t like it.”

“So, he’s going to divide the parts according to your voices and rearrange the song… Huh?”

Oh Dong-cheol blinked and checked the email again.

Yoon Nana clapped her hands together.

“Wow! He’s going to rearrange it for us? When?”

“Something’s not right.”

“Why?”

“He says he’s attached the rearranged sheet music, tailored specifically for you four…”

“Huh?”

Yoon Nana checked the time.

“President, it’s only been 30 minutes since you sent the email.”

“That’s exactly what I’m saying. Something’s off.”

Beside Yoon Nana, Seo Sora clenched her fist and muttered to herself.

‘He just rushed through it because it was a hassle, didn’t he? It’s his little sister’s debut song, and he rearranged it in just 30 minutes? He’s dead when I get home!’

She forced a smile and said,

“President, shouldn’t we check first? Maybe he didn’t fully arrange it, but just suggested a direction for the arrangement.”

“Ah! That makes sense. That would be more realistic.”

Oh Dong-cheol sat in front of the computer, opened the email, and downloaded the attachment.

His computer had several composing programs installed. One of them was the same program used by Seo Jung-woo.

When he clicked the file, the program automatically launched, and the sheet music appeared.

“Huh?”

Oh Dong-cheol blinked again.

Yoon Nana moved closer to check the monitor.

“What? Is it not opening prope—Oh my god.”

Seo Sora also stepped forward.

“What? Don’t tell me he wrote something scolding us for being terrible—Eh?!”

On the screen was a perfectly arranged sheet music.

Not just the melody, but a fully completed instrumental arrangement. Moreover, notes and advice were written all over the sheet.

Yoon Nana couldn’t believe it.

“The sheet music changed this much? This is a fully arranged song! It has piano, guitar chords, electric violin, every instrument’s sheet music. And this was done in just 30 minutes...? Does that even make sense?”

Oh Dong-cheol was also in shock.

“It shouldn’t make sense… But it does.”

For a moment, silence filled the room.

The twins, Park Da-yeon and Park Ha-yeon, stared at the monitor in awe.

“Wow! He even left notes for us.”

“That means he already figured out everything about us.”

Seo Sora made a suggestion.

“Let’s listen to it first.”

“Huh? Oh, right. Let’s do that.”

Oh Dong-cheol pressed the play button on the music program. A fully arranged instrumental version of the song flowed out from the speakers.

As the music played, the four of them sang along to their newly assigned parts. They weren’t singing seriously, just following the melody casually.

The original version had been a bit difficult to sing, but now it was much easier.

And it sounded better.

Much better than when they had tried singing it themselves.

When the song ended, Park Ha-yeon suddenly threw both hands into the air and shouted,

“Praise be to Dimension!”

Park Da-yeon raised her hands as well.

“Lift your hands high and let the music welcome Dimension!”

“We dropped out of college, so if this failed, we were doomed! But we’re saved!”

“Without Dimension, Mom would’ve killed us!”

Park Ha-yeon and Park Da-yeon were high school seniors, but they had given up on studying long ago.

Yoon Nana still couldn’t believe it.

“President, is this even possible? How did he create a song that fits the four of us so perfectly in just 30 minutes…?”

Oh Dong-cheol remembered the sheet music Seo Sora had brought. One was scribbled on the back of another sheet of music, and another on the back of a takeout flyer.

‘So he really wrote and composed everything on the spot?’

Looking at the sheet music, perfectly arranged for the four of them, it didn’t seem impossible.

Oh Dong-cheol swallowed hard and spoke.

“I think… Dimension really is a genius.”

As soon as he said that, Park Ha-yeon and Park Da-yeon raised their hands again.

“Praise be!”

“Dimension has saved us!”