oh lord almighty, i NEVER thought that this manga could turn into something so depressing. I really like how it is shown that, even tho all 3 races have split from humans, they all still are humans with different bodies. they are selfish, seek destruction and salvation, love and hatred, wish to change themselves but also cling to the past. Sensei is truly the most inhuman of all of them, but that only because he feels love to his gems and not much in regards of negative emotions. He is too nice, too calm. The lunarians, the gems on the moon and phos act selfish tho, they want to see their own wishes fulfilled in no regards to others, while the earth gems refuse to see anything from a different light, they are stuck in a limbo of their own worldview.
All in all it seems to me that the whole manga is an analogy to human civilization, different civilizations have different goals and morals, so much that they would go over corpses to achieve their goals. Plus, anyone who crosses the borders between warring nations, cant be seen as a citizen of their homeland anymore, but probably also dont want to join the other nation, leaving them with no place to call home anymore and maybe not even people to call friends or family, perfectly shown through phos.
ok, sorry for rambling so much, had so many thoughts about this manga but no one to share these to, see you next chapter