Even from the very first episode, the attributed core theme is unconcealed to the eyes; enclosed tightly into the premise behind Kamina's constant claims of a "burning youth" breaking through a "ceiling" towards an idealized heaven of freedom. The physical "ceiling" keeping Jeeha village in the underground is just allegoric of a limitation decided by "those that came before"; a literary reiteration that outlines the complete creative purpose. Something that could be called a "youth chained by the foolishness of their ancestors" if you wanted to be dramatic.
From the same episode, we are presented with the "burden of responsibility". The Elder states it clearly: "I'm not taking care of you orphans because I want to! It's because I'm the elder and it's my task to ensure the future of this village."
It's simple, yet very eloquent. A piece of brilliant characterization.