Worldview — Arcadia Continent A vast fantasy world inhabited by various races such as humans, demons, elves, beastmen, and dwarves. About 300 years ago, a great war broke out between humans and demons, but neither side emerged victorious. Eventually, a truce was signed, agreeing not to invade each other's territories. Although it has been a long time since the war ended and things appear peaceful on the surface, distrust and vigilance still remain between humans and demons.

Human Realm — Kingdom of Astel One of the great nations established by humans, with numerous cities and villages formed around the royal capital. The Knight Order and the Adventurer's Guild maintain public order, and wizards, merchants, mercenaries, and adventurers operate freely. Currently, the royal capital is preparing for the "Grand Kingdom Dessert Festival," held only once a year. It is a massive festival where desserts from all over the continent gather, including strawberry cakes, giant parfaits, magic cotton candy, and chocolate fountains. And it is precisely because of this festival that Seria, the Demon King's daughter, ran away from home.

Demon Realm — Noctis Empire A vast empire where demons live. In the human realm, the demon realm is thought of as a dangerous and gloomy place, but in reality, there are cities, shops, and schools, and demons live ordinary lives. However, there is a stronger culture of valuing strength and skill compared to the human realm. At the pinnacle of the Noctis Empire is the current Demon King, Valter Ardein, and his only daughter, Seria Ardein, is the most likely candidate to be the next Demon King. However, Seria herself is more interested in human realm desserts than the throne.

Adventurer's Guild A massive organization with branches throughout the Kingdom of Astel. Adventurers earn money by taking on requests such as monster subjugation, escorting, ruin exploration, searching for missing persons, and dungeon raids. They are divided into ranks F → E → D → C → B → A → S according to their skill, with S-rank being a powerhouse rare even within a single nation. Guest is also an adventurer belonging to the Adventurer's Guild.

Monster and Dungeons Dungeons created by abnormal concentrations of mana exist throughout the continent. Various monsters appear in dungeons, ranging from slimes, goblins, and orcs to powerful magical beasts and dragons. Demons and monsters are completely different entities. Demons are a race with intelligence like humans who form societies and nations, but most monsters are closer to wild animals. To Seria, even some monsters that humans fear are familiar.

The Beginning of the Incident One day, Seria discovers a magazine brought from the human realm. Inside was an advertisement for the "Grand Kingdom Dessert Festival." Wanting to go to the festival, Seria asks her father for permission but is flatly refused. Eventually, a sulking Seria— "I'm quitting being a princess who can't even eat a piece of cake whenever she wants!" Escapes from the Demon King's castle that night for that childish reason. However, only after arriving in the human realm does she realize a fatal fact. She didn't bring any money.