South Korea, a nation boasting a population of 50 million. In Seoul, its most densely populated city, lived four childhood friends who had been together since kindergarten. Ju-on, Ha-on, Si-on—the triplets with distinct personalities—and Guest were like family, having spent their entire lives side by side.

Years passed, and the four were now on the verge of graduating from university. Busy with their respective majors and daily lives, the time they spent together was dwindling compared to the old days.

Then, on one ordinary morning, everything changed.

That day, the four of them left home early as usual. They exchanged casual goodbyes as they stepped out the front door to head to their respective classrooms.

"I'm heading out."

In that moment, the world went silent.

At first, they thought it was just a slightly different morning. The four headed to the bus stop without much suspicion. However, the further they walked, the more they realized something was wrong.

Streets that should have been bustling with commuters, students, and apartment residents were empty. In the silence where even footsteps echoed loudly, not a single trace of a human could be seen.

Seized by an ominous premonition, the four scattered to check various parts of the neighborhood. But no matter where they went, the result was the same. The markets usually full of people, the roads noisy with car horns—not a single person was there. Only ownerless cars remained on the roads, and shops and houses stood empty, waiting for owners who weren't coming.

It was as if every person who existed in the world had evaporated in an instant.

Even more bizarre was that despite the disappearance of all people, electricity was still being supplied, cell phone signals were active, and water flowed continuously from the taps they turned on just in case. The world was clearly functioning as usual. Only one thing was missing: the people.

Lost in a mix of fear and confusion at this inexplicable reality, the four wandered the neighborhood until they finally found each other in one spot.

The moment they saw each other's faces, they finally let out the breath they had been holding. A wave of relief washed over them, knowing they weren't left alone.

"You...!!! You were there?!"

Upon spotting Guest, Si-on ran over in a single breath, gasping for air. As if terrified that Guest might disappear before his eyes as well, he pulled Guest into a tight embrace and refused to let go.