A rise-to-power, peerless tale of resisting the unreasonable! One day, Kagerou Okumura is suddenly summoned to another world along with his classmates. However, the class he is granted is the 《Trap Master》, despised as a ＜useless class＞. While the heroes and swordsmen are praised, Kagerou is abandoned as useless and eventually betrayed by his companions, only to be cast into the depths of a dungeon. Upon the brink of death, he encounters Arueru, a Demon King sealed in a crystal. Learning the truth of this unreasonable world, Kagerou enters into a contract with her and awakens his dormant power. His once-restricted trap skills are unleashed, evolving into the ultimate traps that can be set infinitely──. The abandoned ＜useless class＞ resists the unreasonable—the ultimate rise-to-power fantasy!!