He just agreed to pay a $100k debt. First of all, Ridiculous. Second of all, wtf if there was anytime for a slave narrative to actually make sense in an isekai, this is the situation. She could just be an indentured servant but even if she gave him every gold she made it would still take over 2 years to pay him back, which she wouldn't be able to do. Looks more like a 4+ year situation. Again, ridiculous.
I'm all for good guy MCs saving girls but uh...the author is freaking delusional if he thinks he (or his audience)would give a cute girl a $100k loan and ask for nothing special in return. He could've (and should have) written a much more believable situation.