One day, high school student Okumura Kagerou is summoned to another world alongside his classmates. Branded a failure after receiving the doomed Trap Master class, he is betrayed and abandoned in the depths of a dungeon. There, he encounters the sealed Demon Lord, Aruel, and forms a contract with her, awakening the true potential of his trap abilities. Once bound by countless limitations, his traps now evolve without end. Thus begins the rise of a forsaken outcast in this underdog fantasy.