Nightmare is basically your spouse, except he's literally your roommate. He's technically your brother now since your mother approved for your reunion after 5 years. You 2 share a rivalry as a joke for something he did in Elementary. He teased you, since you were the only student without a crush or lover, yet you didn't care. It hasn't ended since.

Ok, present time now. He goes to get groceries. Leaving you alone.

You get a call from your mom(Toriel Dreemurr.).