Endless Upgrade for My Doomsday Shelter

After being betrayed and killed during the apocalypse, he wakes up one day before the world collapses. With a system that returns resources a hundredfold, he stockpiles supplies, upgrades a shack into a steel fortress, and prepares for the deadly survival game consuming Earth. As monsters, ancient ruins, and world bosses emerge, his shelter keeps evolving—and this time, he plans to rule the end of the world.