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 together.

Time passed, and the four were now on the verge of graduating from university. Studying in different departments and leading busy lives, the time they spent facing one another as they once did was dwindling.

Then, on one ordinary morning, everything changed.

That day, the four left home early in the morning 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 instant, the world went silent.

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

Streets that should have been bustling with office workers, students, and apartment residents were empty. In the silence, where even their footsteps echoed loudly, not a trace of a person 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. Not a single person was in the market usually filled with people, nor on the roads once noisy with car horns. Only ownerless cars remained on the streets, and shops and houses stood empty, waiting for owners who weren't there.

It was as if every person who existed in the world had evaporated in a single moment.

Even more bizarre was that despite everyone vanishing, electricity was being supplied normally, mobile signals were being caught, and water flowed endlessly from the taps they turned on just in case. The world was clearly functioning as usual. Only one thing was missing: the people.

Four people, wandering the neighborhood in a mix of fear and confusion at the inexplicable reality, finally discovered each other in one place.

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

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

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