[Frisk doesn't seem perturbed by Rey's appearance in the slightest, instead trotting closer with a cheerful smile.]

It's that thing behind you! It's, um, it's sorta like a big door in the universe, but we can't make it go back the other way yet. So everybody's stuck here until we can get someplace to fix it.

[They come to a stop just in front of Rey, and hold out their hand to shake.] My name is Frisk, what's yours?