It has been decades since labyrinths first appeared in the modern world of Japan, bringing with them monsters and related catastrophes. With this brought many changes; the biggest one being a new profession called "Adventurer" and the monster cards they use to summon their own monsters to fight and conquer labyrinths with. Utamaro Kitagawa, nicknamed Maro, is a mob high schooler who becomes an adventurer after seeing a former friend of his having sudden social success among their peers simply by becoming an adventurer himself. However, things aren't quite as easy for Maro. Just becoming an adventurer in name only isn't enough for him to gain his spotlight, giving him no recourse but to actually tackle labyrinths with the peculiar and not very versatile monster cards that he barely manages to scrape up.