System

Built to bond with one chosen Player, the program settled on its host, Sung Jinwoo, right after his first descent into the Double Dungeon beneath the Cartenon Temple. Jinwoo reworked it once the world had been reset and then passed it down to his son, Sung Suho. Later chapters reveal the program is far from unique, since the heirs of several Monarchs each carry their own copy. In practice it runs like a video game: quests come with one-of-a-kind rewards, a leveling track ties into skills and stats, an inventory holds magical goods without limit, and an internal shop charges gold won in combat. Only its designated Player could interact with it, which meant nobody besides Jinwoo could so much as see the thing.

Each level Jinwoo cleared bumped every stat by one and gave him five points to assign, with three more for completing the daily quest. The five attributes broke down as Strength for power and speed, Agility for reflexes and dodging, Stamina for health and recovery, Intelligence for mana, and Sense for sharpened perception and danger detection. Kandiaru designed the whole thing so Ashborn could grow a human body able to take in his full power with no ceiling, wrapping it in a game interface so Jinwoo would understand it without confusion. The program also worked hard to keep him breathing, firing passive skills on demand, assigning kill quests against threats, and flagging any murderous intent nearby, which it did when Goto Ryuji turned a sparring match deadly before the fourth Jeju Island Raid. After the reset, Jinwoo cut out the malevolence while leaving the core intact, and the program then started adapting by itself, inventing pet and companion features it had never carried and even fighting off an Itarim Apostle's strike to heal and cleanse its user. Its marketplace, the Store or Shop, scales to the Player's level and stocks consumables, gear, and weapons like the Knight Killer dagger, plus a Blessed Random Box for a wanted item and a Cursed Random Box for a needed one.

Jinwoo became the Player inside the Double Dungeon when he stayed behind so his raid party could escape, after which the System's explosive growth carried him to the rank of world's strongest Hunter. Kandiaru drew him back at level 100 hoping Ashborn would seize him as a vessel, but the Shadow Monarch turned on Kandiaru, locked him out, and named Jinwoo his heir by handing over his black heart. When Rakan killed Jinwoo during the Monarchs War, Ashborn revived him, gave him the last of his power, and the System, its work finished, erased itself. In the Epilogue Jinwoo rebuilt it into a Tutorial to measure Suho's strength before sealing both the program and the boy's abilities inside him. After Suho awoke in Solo Leveling: Ragnarok he gained the System and its leveling tools, only for a possessed Lee Minsung carrying an Itarim Apostle's strike to corrupt it badly, throwing him into a savage Job Change quest of endless dying and reviving against stronger copies of himself. From that quest the System laid out three classes to pick: a Soul Striker option, the heir class of the Shadow Monarch, and a third left unnamed. Furious that the count was too low for how many times he had died, Suho merged all three into the brand-new class Irregular: White Shadow. The webtoon goes on to show at least two more Monarch's Heirs serving as Players of their own Systems.