Dan-Katsu is a legendary role-playing game that allows you to play more than 1021 classes and has more than 400 possible endings! The more we delve into it, the more we discover new ways to enjoy it, new objects... A certain gamer (player name: Zephyrus) is reincarnated in the world of Dan-Katsu, of which he becomes the main character. Overjoyed, he joins the Labyrinth Academy, the place where the main story takes place. He quickly obtains the 'Hero' class, the best in the game, but discovers that the 'Muscle Warrior', a class considered 'for fun' where he comes from, is perceived in this world as a good class?! That the most difficult dungeons have never been conquered?! In other words... he will be able to enjoy this world as if it were a new game! Determined to show everyone what a good class is, he brings together classmates, allows his reserved childhood friend to become an Alchemist, transforms a selfish Princess into a Saint... Now that he has gathered powerful classes around from him, he is ready to conquer the dungeons!