In a world similar to a heroic fantasy role-playing game, Naofumi has become the hero with the shield: he has an exceptional defensive weapon, but which prevents him from attacking, and therefore from gaining experience. To remedy this, he acquires a young slave, Raphtalia, who will become his armed wing... if she manages to overcome the trauma of her past. On a mental level, Naofumi and Raphtalia will also have to be well armed, as a wave of monsters, the Calamities, prepares to sweep over the kingdom...