The Underground (World of Undertale)

FRISK, gone unnoticed, stepped out further towards HEATHER and waved.
HEATHER's face lit up. She didn't see there was another HUMAN here at all. "Oh, hi!" she said, laughing a little. "Were you here before?"
FRISK smiled and nodded.

Sans smiled, happy to see that Heather liked someone. "Frisk, do you know her? Long-lost siblings, perhaps?"

Spoiler

Based off of the theory that the Justice soul and the Bravery soul are related

FRISK looked at HEATHER a little closer. They shook their head.

Spoiler

WAIT. IS HEATHER FROM-

"I recognize the name..." Sans muses. "Oh well."

Spoiler

You said "XD Yes I do"

Anywayyyyy, back to the plot.

"Funny, I feel like we've met before. Anyway, Heather," Said TORIEL, shaking her head. "Would you like to stay with me, in the castle?"

Spoiler

but if you think it's the slurpee musical, then yes

HEATHER'S face lit up. "Yes, please."

Spoiler

Oh gosh

AND WHO CARES

Sans smiles at the exchange. "Toriel, you can't just adopt everyone you meet."

Spoiler

"How can you say that, when I already hand-knitted you this sweater?" XD

"You can't threaten every human you meet, but you do it anyway."

Spoiler

OH SHI

"Not EVERY human. I didn't get to the kindness one. She died IN YOUR RUINS, remember? Great mothering there."

Spoiler

OH SHI

No I did not only just wanted to mock you noooo