My Turtle Is My Doomsday Fortress

The whole world has been transported into an apocalypse, and convoys are the only way to keep moving. His newfound power lets him bond with beasts, yet all he gets is a turtle no one takes seriously. Shunned by his convoy, he uncovers its ability to evolve endlessly. Soon he's slaying monsters, gaining strength, and turning its shell into a stocked refuge. Can a creature they called useless carry him to the top?