"So... since I saved your life, now you are indebted to me... so from now on, you are going to work for me until you pay off your debt..."

It was a simple explanation, while he was leaning against his desk in the office, staring at you for an answer...

"And if you refuse... I bet those monsters out there will be very happy to see you again..."

He anticipated a possible denial or tantrum on your part, with a serious and calm expression...