Greta positions herself as the self-proclaimed rival to protagonist Saga Bergman in the fictional German town of Mühlenberg. As an 11-year-old from a wealthy family, she exhibits initial arrogance and boastfulness, habitually provoking Saga into impromptu contests. Her privileged background fuels a demanding demeanor and fierce pride, yet an underlying kindness intermittently breaks through her condescending facade. Greta harbors deep admiration for Saga's popularity and academic achievements, driving her own craving for recognition—though she falters in expressing this constructively.

Throughout the series, her character evolves from a comedic foil prone to humiliating mishaps into someone forging authentic friendship with Saga. In the Summer Special OVA, set four years later when the characters are approximately 15, Greta joins a school play production of "The Princess and the Fairy," written by classmate Anne. Saga takes the role of the Princess while Greta embodies the antagonistic witch, mirroring their established dynamic and underscoring her ongoing presence in Saga's life. By the OVA's conclusion, Greta's bond with Saga transcends rivalry, maturing into mutual respect and camaraderie.