Willem Kmetsch wakes up from his icy slumber as the last surviving Emnetwiht, a race of humans that populated the planet’s surface until they met their untimely demise five centuries ago at the hands of "Beasts." Currently, he lives among the hundred odd floating islands that make up civilization—otherwise inhabited by various other species, all of whom possess distinct animal-like features such as horns, fangs, wings, and scales. Because he lacks any such feature, Willem is referred to as a "markless." One day, Willem encounters another markless named Ctholly Nota Seniorious. He thinks nothing of the meeting, and continues to spend his days working odd jobs until he runs into her again, this time after accepting a military posting. Willem soon learns that the group of bubbly young Leprechauns he is tasked to look after are pivotal in the ongoing battle against the Beasts. These girls, who have had little exposure outside a world where they are treated as weapons, are willing to die if it means defeating the Beasts. Determined to nurture a life of normalcy for them, Willem soon becomes a father figure to the girls. Just like how he once went off to battle, he must now come to terms with watching these children go off to war. [Written by MAL Rewrite]

Five years have passed since the tragic incident ended the peaceful life on Regul Aire once and for all. The Beast have reached the floating island and are threatening the last survivors. Tiat, Collon, Pannibal, and Lakhesh have become fairy soldiers and are continuing the role of their predecessors, fighting for the safety of Regul Aire. And just like all the other fairy soldiers of the warehouse, they need a guardian of the military, and so on one fateful day, Tiat encounters Feodor Jessman, a young imp and fourth-grade military officer. At the first glance he appears like a typical honor student, however, it's not for long until he reveals his true colors. What will his secret ambitions bring for the four young girls and even the future of Regul Aire?

Five hundred years have passed since the humans went extinct at the hands of the fearsome and mysterious 'Beasts.' The surviving races now make their homes up on floating islands in the sky, out of reach of all but the most mobile of Beasts. However, this new safe haven Regul Aire has a dark secret behind it. Only a small group of young girls, the Leprechauns, can wield the ancient weapons needed to fend off invasions from these creatures. Into the girls' unstable and fleeting lives, where a call to certain death could come at any moment, enters an unlikely character: a young man who lost everything in his final battle five hundred years ago, the last living human awakened from a long, icy slumber. Unable to fight any longer, Willem becomes the father that the girls never had, caring for and nurturing them even as he struggles to come to terms with his new life, in which he feels the pain of helplessly waiting for his loved ones to return home from battle that his 'Daughter' once felt for him so long ago. Together, through their everyday interactions in the 'orphanage,' Willem and the girls gradually come to understand what family means and what is truly worth protecting.