Hearing this, Negris found it absurd yet logical. The cost of governing an undead society is very low, without a need for taxes to maintain it. If there were any shortage of supplies, such as minerals or grains, they would have low-level skeletons farm them, just like Ange does.
Farming skeletons like Ange cost almost nothing. Once they were taught how to farm, they could continue working for decades without rest. There is no need to enslave humans as it would involve management costs, and providing necessary living supplies would be much more troublesome than dealing with skeleton zombies.
The only thing the undead require is human remains, so they supply food from time to time, fearing their malnutrition. As per Serene's words, if it weren't for the undead's inability to produce much, they would breed all humans.
As per the script, once humans mature, shouldn't the undead kill them to get the sturdiest corpses?
