I Become Stronger by Being Beaten in the Last Days

This world is full of radiation that can mutate and kill people. People can only huddle in cities protected by protective walls, but our protagonist, as a person who needs to often go out of the city to receive radiation infection, has a special physique. What? Others can only stay outside for a few hours, but how come I stay out for several days without doing anything but feeling more and more energetic! What? Others were beaten and injured and needed medical treatment. Not only did I not use it, but I also became stronger! Welcome to this wasteland world, explore new things with our protagonist, and become stronger together! This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.