Locked in a suffocating cubicle on Cloud Alpha, Kai is forced to live with Bella's pristine, non-decaying corpse as a test of his submission to the academy. He refuses to break, screaming and punching the steel door until his knuckles bleed. To escape this cage, he must demonstrate acceptance, so he plays the part while using his newly unlocked Legacy Skill, Deep Slumber, on his sister's body. The darkness of the night devours her, feeding her to the House of Night and yielding eight experience points. When Kai finally uses the skill on himself, his consciousness drifts into the House of Night, a silent realm of shallow water, misty expanses, and a faint starry sky. He walks the endless void until he encounters Noxian, a nine-foot-tall shadow warrior with blades for arms. By demanding the warrior's name, Kai triggers an excruciating mental pain that unlocks the Perfect Slash fragment and the Nigh-Phantom imprint. This imprint allows him to become invisible to anyone who lacks direct intent toward him. He leaves his prison with a cold heart, ready to blend into the academy while plotting the downfall of everyone who deemed his existence a sin. The first test of his new power comes immediately at the Eventide Academy, where he is assigned to a dusty basement and targeted by Roan, the arrogant leader of the Ursa Minor gang. In a crowded cafeteria, Roan demands half of Kai's mined ores. Kai responds by grabbing Roan's collar and breaking his nose with a brutal headbutt, launching a chaotic brawl that marks him as a dangerous pariah.

The academy escalates its filtering process by releasing a minotaur-like monster into the dorms. Kai uses his Nigh-Phantom imprint to slip past the beast, eventually teaming up with Matilda to decapitate it with her summoned sword of light. However, Roan ambushes him, and the headless monster throws them into the courtyard, knocking Kai unconscious. He wakes up in a cavern on the cultivated cloud Ixos for the brutal Rite of Blood. In the first trial, Professor Hera forces them to choose between two identical red vials, one poison and one antidote. Kai risks his life by drinking his own vial first. When it turns out to be poison, he swaps with Matilda, who has two poison vials due to a sabotage attempt on her life. In the second trial, the students find only two masks for three people, meaning one must be left to suffocate. A timid student tries to manipulate Kai into fighting Matilda, but Kai exposes him as a cold-blooded killer. During their fistfight, the student pulls an enchanted knife, but Kai disarms him and chokes him to death, discovering an assassin sigil inside his mouth. As they step onto the surface of Ixos, Matilda calculates their low survival odds and betrays Team Crius to join the powerful Team Coeus, led by the barbaric Lion. Left with only the deformed Dorian and the timid healer Abigail, Kai must survive in the wild while hunted by his former classmates.

Hiding in the dense forests of Ixos, Kai focuses on gaining raw power. He uses his accumulated experience points to summon Noxian again in the House of Night. To master the Perfect Slash fragment, Kai must endure a hundred years of simulated sword training compressed into a single moment. The agony breaks his bones and tears his muscles, but his memory of Bella keeps him grounded. He emerges with the slashing intuition and the Dark Discharge imprint, which lets him release explosive mana blasts through his weapon. When Team Coeus transports a massive crate of mined mana ores, Kai, Dorian, and Rakha launch a daring ambush. Kai decapitates a guard and steals sixty-one mana ores, but the monstrous Wolf, a High Angel with the blood of Cerberus, intervenes. Wolf's raw strength is immense, but Kai uses his slashing intuition to bypass his defense, wounding him with a Dark Discharge blast before escaping into the shadows. The victory is cut short when Abigail, driven by fear, betrays their hiding spot to Matilda. Matilda corners Kai with three barbarians, using Abigail as bait while forcing her to wear a lamb mask labeled Bella. Kai's rage boils over, and he parries their blades and slices the limbs off two barbarians before devouring the third with Deep Slumber. He uses their blood to draw a golem symbol on his forehead, completing Perion's quest to unlock the Stone fragment.

Kai clashes with Matilda, whose summoned golden shield and sword of light push him to his physical limits. Using his newly acquired Stone fragment, Kai anchors his body to the earth, increasing his durability. He shatters Matilda's shield and breaks her arm, but the exertion drains his mana, causing him to collapse. Matilda spares his life out of pity and returns to Team Coeus with a fake claim of his death. Kai wakes up alone and devours all sixty-one stolen mana ores. His Primordial Lock absorbs the energy with perfect efficiency, allowing him to bypass the traditional bottleneck and break through directly to Grade 2 Awakened. His strength, speed, and mana skyrocket. He tracks Team Coeus to their camp, where they are besieging Team Hyperion. Kai uses his superior stats and the Dark Discharge imprint to dismantle their forces. He confronts the barbaric Lion, who wields a grade-one enchanted Fire Aegis. Despite Lion's feral Chimera bloodline, Kai's slashing intuition and explosive mana blasts overwhelm him. Kai ignores a professor's intervention and uses Deep Slumber to devour Lion, securing the Blue Gem from the Awakened Monster to win the Blood Rite. He returns to the academy as a conquering force, but the corrupt Chancellor retroactively strips him of his Angel status, fueling his hatred for the system.