Shuumatsu Nani Shitemasu ka? Isogashii desu ka? Sukutte Moratte Ii desu ka?

A long time after mysterious Beasts caused human extinction, Willem wakes up as the last human. A new civilization of different races has developed on floating islands, but Willem, being human, has no place there. After wandering without purpose, he reluctantly takes a military job, only to find out that the "weapons" he is assigned to guard are young faeries. As he learns more about the children and their connection to his past, the conflict with the Beasts becomes more dire. When the girls get ready for a seemingly unwinnable battle, Willem must decide if he can do anything to help.