"WorldEnd" is set in a post-apocalyptic world where humanity has been nearly eradicated by monstrous creatures known as Beasts. The surviving humans have taken refuge on floating islands, protected by a mysterious force called the Fairy Warehouse. These islands are governed by a militarized society that relies on Leprechauns—young girls who wield ancient weapons called Dug Weapons—to fight the Beasts. The Leprechauns are paired with male soldiers known as Braves, who act as their handlers and partners in combat.

The story centers on Willem Kmetsch, a former soldier who was frozen in time for 500 years and awakens to find the world drastically changed. Willem is assigned to oversee a group of Leprechauns, including Chtholly Nota Seniorious, Ithea Myse Valgulious, and others, who reside in a facility on the 68th floating island. As Willem grows closer to the girls, he learns about their tragic fate: Leprechauns are created to fight the Beasts but have a limited lifespan, as their bodies deteriorate rapidly due to the strain of wielding Dug Weapons. Despite this, they continue to fight to protect humanity, even as they grapple with their own mortality and the emotional toll of their existence.

The narrative explores themes of sacrifice, loss, and the search for meaning in a world where survival comes at a great cost. Willem, burdened by guilt over his past failures, struggles to reconcile his role as a protector with his inability to save those he cares about. Chtholly, in particular, becomes a focal point of the story as she develops feelings for Willem and confronts the inevitability of her own death. The series delves into the relationships between the Leprechauns and their Braves, highlighting the bonds they form and the sacrifices they make for one another.

As the story progresses, the characters face increasingly dire threats from the Beasts, leading to intense battles and emotional confrontations. The series balances moments of action and tension with quieter, introspective scenes that delve into the characters' inner struggles. The world-building reveals a complex history of conflict and survival, with hints of deeper mysteries surrounding the origins of the Beasts and the true nature of the Fairy Warehouse. Through its exploration of love, duty, and the fragility of life, "WorldEnd" presents a poignant and thought-provoking narrative.