Oh dear, where do i begin?.. All of this is just like human nature, this whole manga in fact is an analogy of humanity. This chapter in particular. Phos and the others are on their way to shatter the earth crystals into pieces for their own goal. The earth crystals just wanna have fun and enjoy life, oblivious about the interests of phos, or they just dont care.
It's a lot like war, if you think about it. Both sides have goals which the other dont understand or dont care about and in the end, phos is becoming what they hated in the first place, the lunarians. The invaders, who come in regular intervals to make life hell for the earthlings. They became like this through betrayal from their earth friends and through alienation from the lunary crystals. It's really damn depressing if you think about it. Belonging to none, having nowhere to call home and ONLY because you wanted a quiet life with your friends. That wish costs you your home, your friends and your sanity. We would probably end ourself bc we dont see a future anymore. The crystals can't do that. Neither can Adamant nor the lunarians. It's a tale of immortality, the loss of sanity and the journey from being happy, cheerful and oblivious to depression and suicidal tendencies with a deathwish for every living thing...
Sorry to ramble here, have to collect my thoughts on this masterwork of a manga but have no one to talk to :v