@aleaallee Id rather say its a series, where the author actually gives a fu*k about world building and makes the isekai stuff meaningful.
Basically 99,9% of the other isekai series either just kill the mc off or transfer him in the beginning of the series and never came back to why. 10+ years ago this was just called fantasy story, but now they just add the 3 pages isekai plot to market their product with an "isekai lable", though its just another fantasy story rip off.
I read my first isekai as a kid 20+ years ago, when the term didnt even exist (Neverending story). This story is the first Japanese work actually coming close to this one.