Chapters 3 through 12 of the light novel detail Tio's dramatic expulsion from the Hero Aira's party and his subsequent journey to become a powerful Black Magician.
The narrative begins with Aira, a beautiful and determined Hero, coldly informing Tio, her childhood friend and knight, that he is no longer needed and is being kicked out of the party. Lucius, the party's High-class White Mage, cruelly reinforces this, calling Tio a hindrance. Tio, though hurt, accepts their decision, understanding his Mid-class Knight abilities have fallen far behind Aira's Super-class Hero and Lucius's High-class White Mage. He leaves, heartbroken but still wishing them well on their quest to save the world.
That night, Tio has a vivid dream of a past life. He witnesses a battle between a powerful demon and a man named Schwarz, known as the Magic King, who wields Black Magic. Schwarz defeats the demon with overwhelming power, and Tio awakens with the memory of being Schwarz. He realizes that the "bottom-tier" Black Magician class, which he was previously offered as his only alternative to Knight, is actually a path to immense power. Driven by his desire to still help people, Tio resolves to change his class.
At the Adventurer's Guild, Tio's request to change from Knight to Black Magician is met with disbelief and mockery from the receptionist and nearby adventurers, fueled by Lucius's likely gossip. Despite their scorn, Tio successfully undergoes the class change. Afterward, he purchases a large quantity of Potions and is immediately confronted by Iris, a beautiful Elf Sword Saint and an A-rank adventurer. She dismisses him with contempt for his class change, but Tio, focused on his new path, barely registers her insult.
Tio then begins a unique training regimen. He visits the market and repeatedly uses his new Black Magician skill, "Black Drain," on various fruits, vegetables, and even small animals, consuming a Potion after each use to restore his magic. This process, repeated for 666 different life forms, unlocks three "EX Skills": Black Bullet, Black Javelin, and Black Storage. These skills are far beyond normal class abilities, hinting at the true potential of Black Magic.
He then ventures into a nearby labyrinth to test his new powers. He easily defeats E-rank Slimes with Black Bullet, which drains life force. He progresses to the third floor, encountering D-rank Orcs, which he dispatches with Black Javelin, a powerful and fast-piercing attack. He also utilizes Black Storage to efficiently collect the defeated monsters.
Reaching the tenth floor, Tio discovers Iris, injured and cornered by two A-rank Lesser Dragons. Despite her earlier disdain, Tio immediately intervenes, swiftly defeating both dragons with Black Javelin. Iris, stunned by his power, is shocked to learn he is the "expelled Black Magician." She is also strangely captivated by him, her initial contempt replaced by admiration and a growing affection.
After the rescue, Tio and Iris return to the Guild. Iris, now completely devoted to Tio, clings to him, much to the astonishment of other adventurers. Tio, though flustered by her behavior, reports the unusual appearance of A-rank monsters on the tenth floor. He then registers as an adventurer, receiving an E-rank Adventurer Tag, and sells the Lesser Dragon corpses for a significant sum of white gold coins.
Iris insists on accompanying Tio, leading him to a luxurious inn. There, she confesses that Tio is her first love, confessing her feelings after he saved her life despite her earlier rudeness. Overwhelmed and inexperienced with such declarations, Tio proposes they form a party to travel together and get to know each other better, which Iris joyfully accepts.
Their journey together begins with a celebratory dinner. Iris questions Tio about his unique Black Magic skills, and he explains their existence is due to a special method known only to him. Later, after a night where a drunken Iris clings to him in her sleep, they visit a weapon shop. They meet Val, a cheerful Tiger-eared blacksmith, who sells Tio a powerful staff and a secondary short staff. Iris, having upgraded her armor to a revealing bikini armor to maximize her speed, is thrilled to fight alongside Tio.
In the labyrinth, Tio and Iris demonstrate impressive teamwork. Iris, with her enhanced speed and dual swords, swiftly dispatches goblins and orcs, while Tio supports her with his EX skills. Their coordinated attacks are highly effective, and Tio unlocks two new EX skills: Black Summon (Magic) and Black Summon (Mechanical), hinting at even greater power to come.
