When he woke up, he finds himself reincarnated into the world of the epic RPG "Spirit War Dungeonmage". However, he is not the main character, not even some mob NPC.His abilities are modest. His skills are clunky. His only catchphrase is "Hyahaha..."He has been reincarnated as a shitty, first-level mini-boss who is supposed to die in the tutorial!He realizes that he will be caught in a doomed ending soon, and when he discovers that even his beloved sister will die of illness...."I've made up my mind, sister. I'm going to crush all the unreasonable premises of this world."The man decides to rebel against the official history (plot) by utilizing his vast knowledge of the game. And so, he "conquers" the bosses of this world, even the strongest backstage boss and the most traumatically difficult final bosses in the game......, until he finally...!