The Siege Engine

When the world ended, humanity hid. Jaxen Vance built a wall. Fifty years after the Convergence turned Earth into a monster-infested wasteland, survival belongs to whoever has the strongest walls and the biggest army — and Jaxen has neither. What he has, after his settlement is slaughtered and he's left for dead in the ruins, is a glowing crystal and a System class nobody has seen in a decade: Aegis Warden. While everyone else levels up by fighting, Jaxen levels up by building, turning scrap metal into plasma turrets, dirt into acid moats, and a ruined shack into a Tier 5 Bastion that grows stronger with every attack it survives. But a warlord wants his Core, a Broodmother is organizing a horde of ten thousand, and the fortress that should be more than enough is about to be tested by an apex predator that has been evolving specifically to break it. Perfect for fans of Defiance of the Fall, Dungeon Crawler Carl, and The Primal Hunter — this is progression fantasy where the power fantasy is earned and the base is the character.