"It's about a fantasy world where humanity was fighting all the other races. Humanity was using "heroes" who had sacred swords with very specific technology. Those swords allowed the human race, considered as one of the weakest, to actually stand above others. The main char was one of the heroes who went to the last battle against the stellar God-who was leading the other races-. When he wasn't fighting, he was the "father" of an orphanage (a normal one on earth).
They won, but the heroes are pretty much wiped out with that last battle. He get turned into stone himself. Top be awakened 500 years later. And learn that humanity was wiped out by another problem since long ago, and that the other races are surviving by living on floating islands, since the world itself cannot be lived in anymore. Some salvager, who go to the surface to get ancient technology (especially those famous holy swords) found him and "reanimated" him. As the last survivor of humanity, he'll find himself managing young girls used to fight the new menace. They are considered expandable, and can be ordered to detonate themselves if necessary to save the floating islands. That race has a particularity to not care about their own life, so they're fine with it. He cannot fight anymore by himself, since his body's inside are pretty much a mess. So he will try to bring them to want to live, and will try to rise the chance of them returning alive from battlefield. Rather than being on the battlefield, we see the MC as he's worrying about the girls that went in the battlefield, for example. So there is little to no action, that's not the point of the series."

http://i.imgur.com/BZ0ECCL.jpg

I am now lending a helping hand for the girls’ ending.
This is an ephemeral and wistful story of girls called “fairy weapons” and a surviving “quasi-brave.”
In the world after the land is trampled down by unidentified monsters “beasts” and many tribes including human beings are destroyed, the tribes who have barely survived leave the land and are living in the flying archipelago called “regles-aile”
Willem-Kmetsch, waking up in the sky 500 years later, has lived like a hermit in despair, because he could not protect what he wanted to, or even worse, has survived alone when all others died. In the meantime, he encounters some girls through the job of weapon maintenance that he has started unexpectedly.
Chtholly-Nota-Seniorious is one of the fairy soldiers, a girl who can wield the strongest holy sword. In return, she is eventually doomed to lose her life. Having accepted such a fate, she starts to change her mind by encountering and becoming attracted to a young man Willem-Kmetsch. Nevertheless, she leaves for the battlefield, which is heart-wrenching.
What kind of ending will be waiting for this strong, but fragile “end-of-the-world heroine?”
Would it be alright if I wished to stay alive?
Would it be really alright if I had such a dream?

https://pbs.twimg.com/media/C9Hc0s7VwAAb4ZU.jpg