Keppi reigns as the prince of the Kappa Kingdom, a white quadrupedal kappa distinguished by a flattened yellow beak and a life-sustaining sara—a circular indentation atop his head crowned with triangular pale green material. His stumpy legs transform into muscular limbs when extracting shirikodama, mythical organs housing desires within their hosts’ rectums. After the Otter Empire crushed his kingdom, Keppi’s shirikodama fractured: the despair half became Dark Keppi, a weapon enslaved by the Otters, while his diminished chibi form was imprisoned in an Asakusa statue until freed by Kazuki Yasaka and Toi Kuji. Tasked with thwarting Otter-created zombies, Keppi converts Kazuki, Toi, and Enta Jinnai into kappa by removing their shirikodama, dispatching them to collect Dishes of Hope from defeated zombies. These dishes grant wishes but demand the trio unite to produce "Sarazanmai," a ritual forcing vulnerable truth-telling.

Central to his story is Sara Azuma, a kappa princess and idol serving as a Greek chorus while sharing a romantic bond with Keppi. The spin-off manga reveals her as the adoptive daughter of Reo Niiboshi and Mabu Akutsu, former Kappa knights turned Otter agents whose quest to repair their fractured relationship clashes with Keppi’s mission. Though prone to anger and impatience, Keppi meticulously guides his allies and ultimately sacrifices himself to resurrect Reo and Mabu after their deaths, embodying redemption.

Anchored in kappa lore, Keppi’s design reflects traditional traits—dependence on his sara’s water and the shirikodama’s symbolic weight. His narrative intertwines desire, connection, and societal manipulation by the Otter Empire, which operates through the corporate entity "Kappazon, Inc."