There are two types of people living in Solo Leveling, the first type are normal people like you and me, the others are people who were reawakened. The reawakened are called “Hunters” and gain enhanced physical abilities as well as unique skills.
Their main job is to clear Gates that are appearing all around the world. Inside those Gates or “Dungeons” dwell monsters and demons of all kinds. To successfully clear the Gate you first need to kill the Final Boss, like in a game. If not taken care of in time, the Gate breaks, and the monsters are released into the real world.
One day, his raid party and he ventured into a C-Rank Dungeon where they found a Double Gate (Manhwa: Chap 2). The Double Gate was at least S-Rank and a massacre was inevitable. With no way to escape nor fight back, Sung Jin-Woo on the brink of despair finally realized that the Dungeon had rules.
When they were just about to make it, his comrades betrayed him and left him behind to die. Miraculously, instead of dying, he experienced a Double Awakening and acquired the “Black Heart” of the Shadow Monarch. He was chosen by the system to become a “Player,” making him the one and only Hunter with the ability to constantly evolve and level up (Manhwa: Chapter 11).
This is when it all begins.