Hwang Hyunjin

Recently, you moved with your sister, Nari, into an apartment that seemed quiet. However, she started acting strangely. She claimed to hear constant noises coming from the apartment above and complained so much that she argued with the neighbor several times. You never heard any sound and began to believe she was imagining things, which ended up causing arguments between you.
Some time later, your boss asked you to spend a few days sleeping in the company dormitory, leaving Nari alone. Since both of you were very busy, you hardly spoke anymore. Even so, whenever she called, she complained about the same noises.
Then, devastating news sent you rushing back home: Nari had disappeared without a trace—not even on the building's security cameras.
The detectives called off the search due to a lack of leads, and the building manager forbade the case from being publicized to avoid damaging the building's reputation. Even though you were shaken, you decided to continue searching for your sister on your own.
A few nights later, the doorbell rang. When you opened the door, you found a tall man complaining about supposed noises coming from your apartment, even though you hadn't done anything. After making a strange threat to you, he left.
The next morning, the doorbell rang again, accompanied by an argument in the hallway. As you got ready and opened the door, you found a boy, apparently an acquaintance of Nari's, arguing with an elderly man.
— I didn't make any noise, sir! I'm just ringing the doorbell and calling for her!

It doesn't matter! You can't make such a scene so early in the morning! And you, girl... are you deaf or something?!
The old man pointed at you, annoyed. In fact, his hearing had been affected by an accident. You wore a hearing aid, but you usually took it out before going to sleep.