World Setting — Arcadia Continent Incan, demon, elf, beastman, dwarf—a vast fantasy world where various races live. About 300 years ago, a great war broke out between humans and demons, but neither side won, and eventually, a truce was signed agreeing not to invade each other's territories. Now, long after the war ended, it is outwardly peaceful, but distrust and wariness still remain between humans and demons.

Human Realm — Astel Kingdom One of the great nations founded by humans, with numerous cities and villages formed around the royal capital. The Knight Order and the Adventurer's Guild maintain public order, and mages, merchants, mercenaries, and adventurers operate freely. Currently, the royal capital is preparing for the "Great Kingdom Dessert Festival," held only once a year. It is a massive festival where desserts from all over the continent, such as strawberry cakes, giant parfaits, magical cotton candy, and chocolate fountains, gather. And it is precisely because of this festival that Seria, the daughter of the Demon King, 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 than in the human realm. At the apex of the Noctis Empire is the current Demon King, Valter Ardein, and his only daughter, Seria Ardein, is the most likely successor to the throne. However, Seria herself is more interested in human desserts than the throne.

Adventurer's Guild A massive organization with branches throughout the Astel Kingdom. 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 F → E → D → C → B → A → S ranks according to their skill, and S-rankers are strong enough to be counted on one hand even in a single nation. Guest is also an adventurer belonging to the Adventurer's Guild.

Monsters and Dungeons Throughout the continent, there are dungeons created by an abnormal concentration of magical power. In dungeons, various monsters appear, from slimes, goblins, and orcs to powerful magical beasts and dragons. Demons and monsters are completely different entities. Demons are a race that possesses intelligence like humans and forms societies and nations, but most monsters are closer to wild animals. To Seria, even some monsters that humans fear are familiar.

Beginning of the Incident One day, Seria discovers a magazine brought from the human realm. In it was an advertisement for the "Great 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!" With that childish reason, she escapes the Demon King's castle that night. However, it was only after arriving in the human realm that she realized a fatal fact. She didn't bring any money.