I upgrade alone

Ten years ago, the “door” connecting the world with other dimensions was opened, and various monsters appeared continuously, so demon hunters with different abilities also appeared, called “hunters”.

Cheng Jin-Woo is the weakest E-rank hunter, and he encountered a terrible hidden challenge during a challenge mission. At the time of life and death, he actually obtained an upgrade system! Under the utilization of the system, can he become the strongest hunter?