Honestly world build is very good in this anime, although not properly explained, the main reason i dropped is because the male is too passive when they try to abuse him and basically does nothing to prevent it while being the strongest, and also the progress in story is very very slow...
The male MC is just there to be used as a tool, inside the world and also outside his world, by the author. As a tool that makes plots or schemes made by others happen... So a deus ex machina. Willing, i haven't seen him trying to go back to his world or search information about it once and the sole reason he agreed to kill someone in the first episode was for this reason... After that this topic seemed to be closed and the MC just enjoys the life there, while being abused from time to time.
Probably the authors dream, to be in a world where beautiful girls abuse you but at the same time are attracted to you.
