The Perfect Plan to Avoid the Death Ending

"I am Herreith Eckbert. You are the one who woke me up." "...Sorry? Who are you again?" "Pleased to meet you, Master." I accidentally ended up unsealing a demon. And to top it off, I got tricked into a fraudulent contract? "This contract remains valid until your death." "...Excuse me?" "It's a lifetime contract, my naïve young lady." "...But I'm terminally ill." His blue eyes wavered in shock. At this point, I'm not sure who's really been scammed here. (Source: Feelyeon Management, translated)