Sword God from the ruined world

I am a swordsman from a ruined world. I accidentally infiltrated a weak human’s body and promised to protect his family in exchange for taking over his body. And I vowed to protect this world. I will never make the same mistake again. If you don’t want to die, stand behind me. The cold wind will become a warm wind, and monsters will become magic stones to accumulate wealth. I am now a swordsman and an S-class hunter.