On her way to school, Aoi, who can see ayakashi, encounters an ayakashi she's never seen and is abducted to Tenjin-ya, an inn in the hidden realm. There, she learns that her grandfather promised that she'd marry the master innkeeper to pay off his debt.
So you're collateral for 
his loan, so to speak.
Man könnte sagen,
du bist ein Pfand für seine Schulden.
Así que estás aquí
como efecto colateral de sus deudas.
En d’autres termes,
tu es une garantie.
Então você é a garantia
do empréstimo dele, por assim dizer.