The world of Duel Masters is one of five great civilizations. Through a card game, duelists can bring these worlds into existence, making what was previously abstract into reality. These skilled duelists are known as Kaijudo masters. Shobu Kirifuda is the best player at his local playground, and seeks to become a world-class master like his father. His first step on the road to conquest begins with winning a local tournament. Rather, it should have, except he is destroyed by the best Kaijudo master in the world, Knight. Shobu loses, but upon remembering the words of wisdom his father instilled into him, decides to continue on the road of becoming a duelist who can enjoy the game for what it is. And so begins his journey to victory－and as we all know, the journey is the most important part!

It is business as usual in the massive city of Orario, where legions of adventurers gather to explore the monster-infested Dungeon. Among them is the easily flustered yet brave Bell Cranel, the sole member of the Hestia Familia. With the help of his demi-human supporter Liliruca Arde and competent blacksmith Welf Crozzo, Bell has earned the title of Little Rookie by becoming Orario's fastest-growing adventurer thanks to his endeavors within the deeper levels of the Dungeon. Dungeon ni Deai wo Motomeru no wa Machigatteiru Darou ka II continues Bell's adventures as he tries to bring glory to his goddess and protect those he cares about. However, various familias and gods across the city begin to take notice of his achievements and attempt to add him to their ranks.

Upon his run-in with a Vouivre—a monster known to be very dangerous—Hestia Familia's captain Bell Cranel is struck with incomprehension. Despite its preceding reputation, the supposed bloodthirsty creature happens to be crying and flees from a group of adventurers. The monster, taking the form of a terrified little girl, prompts Bell to swiftly decide to hide her. Unbeknownst to him, this act of kindness will cause massive repercussions that will soon echo throughout the entire city of Orario.

After having descended upon this world, the gods have created guilds where adventurers can test their mettle. These guilds, known as familia, grant adventurers the chance to explore, gather, hunt, or simply enjoy themselves. Dungeon ni Deai wo Motomeru no wa Machigatteiru Darou ka Gaiden: Sword Oratoria begins in Orario, the lively city of adventures. The Sword Princess, Ais Wallenstein, and the novice mage, Lefiya Viridis, are members of the Loki Familia, who are experts at monster hunting. With the rest of their group, they journey to the tower of Babel in hopes of exploring the dungeon underneath. Home to powerful monsters, the dungeon will fulfill Ais's desire to master her sword skills, while bringing Lefiya closer to her dream of succeeding Riveria Ljos Alf, vice-captain of the Loki Familia, as the most powerful mage in the land.