As far as I can tell, the series stars a bunch of gemstone-based beings that are given life and movement by organisms powered by sunlight. The story's protagonists are these gem-based beings. Their enemies are silent and perfect beings from one of the planet's moons, who come down periodically and try to capture the gems. When they capture them, they break them into pieces and use them as weapons.
I picked out a couple sample pages I really liked. You can actually spot this first one in the preview for the anime (panels go from right to left, and the page number is on the bottom left):
The enemy general (?) has just had their head cut in half, but instead of killing them it only reveals their next weapon: the broken pieces of a captured gem warrior, turned into arrows.
This next page shows one of the volume's weirdest battles (that I've seen so far). Cinnabar is a tragic character who can't safely be around the other gems - they (the characters appear to be genderless) can't help but produce a poison that destroys everything around them, including other gems. A few vague statements in the manga and a glance at the Wikipedia page on cinnabar tells me that the poison is probably mercury. Here Cinnabar is literally fighting the enemy by vomiting poison everywhere.