I randomly discovered this manga and binged the whole thing in 4 hours? I will lay it out, the bizarre comments of people of random websites disapproving slavery of this title in Isekai all seem new to this hobby? Oddly enough this isnt even the worst one, the WORST manga is the Isekai where female students summoned to the other world are brainwashed as sex slaves for life. aka ASTRO KING It is common sense to a seasoned Manga/Manhua/Manhwa reader, every single Isekai themed series will naturally and possibly include slavery. Examples: So I'm a SpiderSkeleton Knight in Another World
Harem in another World
Black Summoner
and the common one "Shield Hero"

This list is nothing but an introduction, I understand this speciifc series integrates slavery on a more cruel scale. But this much should be expected, people can easily forget a fantasy world in Isekai is still a "fantasy" world. If you feel offended, hurt, or disgusted by a series which visualizes the reality of slavery, then you are a massive SOFTIE.

Ochikobore Kuni story wise is super epic, the adventure and scale is done at an impresssive scale. The MC is not only reasonably strong, he sticks to his values and creatively finds ways to improve. In this manga alone, I admire the creative use of combat and magic as there are methods I have never knew of.
Plus he is a great guy, he looks after others, and makes sure to stick a hand out to help whenever it's possible. After reading this, your perception on slavery will change as it's value is priceless in specific scenarios

This is how you do an Isekai on a larger scale that makes sense and doesn't feel bland or boring.