"They are. Family," they tell him again, expression going from bright grin to something a little more...awed, maybe.

Family. What a weird concept. Frisk's still honored they reached out and allowed that--wanted that, after knowing each other so well, and improving their connections with Sans. A human. Someone they were made to kill--and that reminder slips their expression into a scowl until they remind themselves it's fine. It's fine now. They're here again.