The story begins with a magical summoning class at school, led by a specialized palace mage named Gratt.

He introduces two types of summoning magic: one where a connection is formed with a monster, and another where a creature is called forth from a magical circle to form a contract. The students attempt to summon creatures and make contracts with them. Kain von Silford, the protagonist, is encouraged to participate. He pours an excessive amount of magic into his summoning circle, resulting in the summoning of a terrifying being that calls itself the "Prince of Darkness." Despite the unexpected summoning, Cain forms a contract with this demon, who now goes by the name Seth—much to the dismay of the academy staff and his family.

Shortly afterward, Cain is promoted by the king to the rank of Viscount and entrusted with the governance of a city. However, the joyous celebrations are interrupted by alarming news. Signs of a "Stampede" have been observed in the Monster Forest—a phenomenon where monsters go berserk and breach the forest's boundaries. Kain, now an A-rank adventurer, decides to investigate.

He ventures into the forest, accompanied by his summoned creatures, Haku and Gin. They notice an unusual sensation of being watched and attribute the strangeness to a massive gathering of high-level monsters deep within the forest, converging around an "overwhelming presence." To investigate further, Seth summons Dalmatia, one of his subordinates specialized in reconnaissance, who confirms the existence of a fearsome entity deep in the woods.

The episode ends with Kain returning to the city to warn his fellow adventurers, Claude and Lina, about the threat in the forest. Despite the looming danger, Seth and Dalmatia seem intrigued and remain in the forest to continue observing the situation.