Seiichi Hiiragi is a Japanese high school student frequently bullied and regarded as a loser. His entire school is unexpectedly transported to a fantasy world resembling a video game environment with swords and sorcery. During the transition, he accidentally consumes the Fruit of Evolution, triggering a dramatic transformation in his physical abilities, intellect, and overall existence, beginning his journey from outcast to overwhelmingly powerful. Consuming the Fruit grants him extraordinary cheat-like abilities, exceptional strength, formidable spells, and combat skills. He earns titles like "Nightmare of All Monsters" after effortlessly defeating large groups of high-level demons. Despite his power, he occasionally expresses unease about his humanity. He travels with companions Saria, Lulune, Artoria, and Origa. After annihilating a demon horde attacking a capital city, the archmage Barnabas Ablitt recruits him as a teacher at the Barbador Academy of Magic. Seiichi agrees on the condition his companions accompany him: Saria and Lulune become students, Artoria serves as a combat instructor, and Origa acts as his assistant. Assigned to teach Class F, a group deemed problematic and academically challenged where many cannot use magic conventionally, Seiichi's own experiences as a bullying victim shape his teaching approach. His reunion with former classmates attending the academy as "heroes" creates personal tension due to their history. A primary conflict arises when the evil cult The Great Devil Order plots to resurrect a dark deity by sacrificing the academy's students. As the most powerful individual, Seiichi becomes central to thwarting this plan and protecting his companions and the world. His role expands beyond teaching to confronting the cult.