What Do You Do at the End of the World? Are You Busy? Will You Save Us?

A light novel series by Akira Kareno, illustrated by ue. Centuries after monstrous Beasts drove humanity to extinction, Willem — the last human, roused from a long sleep — takes a military post overseeing what he's told is an armory on a floating island. He finds instead a group of young Leprechaun girls who are themselves the only weapons capable of fighting the Beasts, and is drawn into their lives as the war against them grows more desperate.