Lowest Ranked Harbinger is the Shadow Monarch.

One day, after a brutal encounter in an overpowered dungeon wipes out his party and threatens to end his life, a mysterious System chooses him as its sole player: granted the rare opportunity to level up his abilities, possibly beyond any known limits.

Follow his journey as he takes on ever-stronger enemies, both human and monster, to discover the secrets deep within the dungeons and the ultimate extent of his powers.