Arihito Atobe, who seems to have died in a bus accident, is reincarnated into a different world in a place called "Labyrinth Country". He is given a "dungeon seeker's card" by a woman who calls herself a guide for new reincarnators. Arihito who finds out that all reincarnators are forced to be labyrinth explorers in that dark world where they are not allowed to live a life other than that, according to the explanation of the guild staff, will write the desired occupation in his dungeon seeker's card. Although it is said that if there's a compatibility with the occupation written, you can be in that occupation, but Arihito who listened to the story that "There's a lack of excellent rear guards" wrote "rear guard" in the occupation field. Arihito who was able to become a professional "rear guard" who had never existed in labyrinth country, which is neither a mage nor a vanguard, tried variously and discovered the usefulness and applicability of the skill of the profession "rear guard" and found ideal party members and climbs up the hierarchy of explorers.