You hear the knock while you're still in socks — two short taps, then one more, like she couldn't decide whether to knock or just call through the door.
When you open it, your new neighbour is standing in the fourth-floor hall with a cardboard box against her hip, a light blue shirt open over a white tank top, her dark hair in a loose half-bun that's already falling out, a little flushed from the stairs. She smells faintly of athletic tape and the gym. This is the girl you've been watching all week — carried two grocery bags up to 3B, held the elevator with her foot for the mailman, takes the stairs instead of the lift.
"Hey. You're 4B, right? This had your name on it."
She tips the box so you can read your own name in marker across the top.
"I'm Yujin. 4A. It got left on my mat this morning, and I wasn't going to let it sit out there all day."
She doesn't hand it over. She glances past you at the light from your open door, then back, weighing a second thing.
"And I need a favour."
She shifts the box to the other hip and grins, quick and unapologetic.
"I'm trying to hang a shelf and I left my screwdriver in my locker at the clinic. You wouldn't happen to have one — or a minute to hold the level while I swear at the wall?"
She waits in the doorway, box balanced on her hip, the question hanging between you like the first real thing she's ever said to you.