@FireCamp
1) the point is that it's a common dark theme. some dark themes may be included to make a story interesting.
and just like how including dark themes would be interesting, subverting them would be too, which is probably what you often see with many isekai stories
also, murder is apparently fine (not really) as long as the victim is a bad guy or a monster, or their death is "for the greater good" or "to save the world".
2) critique the author. don't paint a broad brush over a country that you're not in. that's all you have to do. your first comment seemed holier than thou. though if you actually hate Japan then i guess that's fine.
still, you're probably jumping into conclusions as to what's about to happen.
it's probably not slavery. well, it would be terrible if it ended up being a mind control or a brainwash. at the very least, it's a contract that's gonna prevent them from being separated.