Slight spoilers ahead on the themes in the anime.
What started out as a seemingly regressed, but peaceful, society, turned out to be so much more than that. Every episode presented a dark twist into what happened in their history or what they've been doing behind the scenes to keep a seemingly peaceful society. Methods such like population control, genetic manipulation, brainwashing, selective breeding, and other things to keep everyone as docile sheep.
Definitely very thought provoking and kept me interested from beginning to end.