The narrative begins with a brutal subversion of the classic hero summoning trope when the dark mage Mordus Kizor sacrifices thirty-two naked slaves to summon a savior for his dark god Loki. The moment Quasi materializes in the underground cavern, he does not offer gratitude. Instead, utilizing his thousands of years of combat instincts, he immediately betrays his summoners. Quasi tightens his grip on Mordus's hand, crushing the old man's bones before driving his knee into the mage's face with superhuman speed, fracturing his skull. In one fluid movement, he rips the dark staff from the dying elder and hurls it like a javelin through the throat of the son, Beurnim, disrupting his spellcasting. The sudden slaughter of these high-level mages triggers a massive system error because the system attempts to rank up Quasi's already maxed-out Hero class. To resolve the conflict, the ancient synthetic soul administrator SAS11, which manifests as a giant floating eyeball, halts time. SAS11 bypasses the system's hardcoded restrictions to grant Quasi the secondary class of Necromancer. Quasi immediately uses his new skill, Raise Undead, to take control of Mordus's level 87 skeletal bruisers. He easily overwhelms the undead's willpower of 227 with his own willpower of 3047, establishing his first vanguard. Quasi then claims Beurnim's ring of enslavement, linking his fate to the surviving, terrified priestess Jessica, whose collar will kill her if she moves more than half a mile away from him. Quasi's ruthless pragmatism sets the tone for his journey, showing that he will exploit any system rule to build his army. He then goes upstairs to slaughter the remaining dark mages, including the muscular pirate Corazon, using the dead mages' bones to repair his skeletons with the Bone Renewal skill.

Quasi leads Jessica into the forbidden fog of Vetiti Spiritus, which is actually the entrance to the first floor of the dungeon iNAEQUO. While the fog's soul-sleep magic immediately knocks out Jessica and his spider companion Peter, Quasi's massive willpower stat allows him to resist the effect completely. Inside the dungeon, he encounters the Gejada, a race of powerful lizard people led by the geomancer Anathema and guarded by Zorren, a level 173 Berserker. To establish dominance, Quasi unleashes a massive wave of mana, levitating dozens of bone shivs around Zorren to prove he is a predator rather than prey. After taking the Enchanter and Noble classes at the dungeon stone, Quasi trains the Gejada guards into the Soldier class, teaching the fighter Thorous the martial art of blade dancing. To secure passage to the second floor, Quasi and Zorren confront the floor guardian Lacerta, a level 117 armored beast. Quasi uses his flying Desbats to blind the monster with their claws, allowing the berserk Zorren to deliver a skull-cracking blow with his bone club. Quasi immediately resurrects the boss as a loyal minion. He then discovers a massive system exploit: by using his Skeletal Renewal skill to heal Lacerta, he can continuously rip off the boss's high-quality bone scales and regenerate them using the surrounding debris. This gives him an infinite supply of high-grade raw materials to craft enchanted weapons and shields for his growing Gejada army, effectively breaking the dungeon's economy before they descend. This exploit proves that Quasi's real power is his ability to treat the system's physical laws as a sandbox, turning a terrifying floor guardian into a literal factory.

Descending to the second-floor jungle, Quasi recruits a dim-witted minotaur named Groknak and establishes a heavily fortified wooden camp. His plans are disrupted when Thorous is forced to fight the minotaur Chieftain Dorkoon, defeating him in a duel and earning the loyalty of the Hard Rock tribe. Quasi raises the dead chieftain to terrify Groknak into submission, but his progress is halted when he discovers a conflict on the third floor. He flies his Desbats to the centaur city of Equus, where the garrison led by the veteran Dragkenoss is being massacred by a massive swarm of Thrashers and their level 139 boss, Berosus. Quasi joins the fray, but his plan fails when his enraged Skeletal Guardian crumbles due to a lack of muscle tissue, leaving him vulnerable. Berosus strikes Quasi, breaking his arms and cracking his ribs. Just as the boss prepares to deliver a fatal blow, Peter the spider reveals his true identity as a level 178 Weaver, transforming into a house-sized arachnid to battle the boss. Jessica heals Quasi's broken bones in minutes, allowing him to launch a coordinated counterattack. Quasi uses his flying undead to choke the boss with its own webbing, suffocating the beast. The display of absolute power forces the legendary Dragkenoss to kneel and pledge his allegiance, giving Quasi control of the centaur cavalry for his upcoming conquest of the fourth floor. This victory cements Quasi's status as a living legend among the dungeon's denizens, setting up his next move against the kitsune.