Ruka Essenpolka is a 9-year-old actress and member of the Excellent Idols, a group of top-tier performers kidnapped by aliens and whisked away to an interdimensional competition. She collects stuffed animals and maintains an unfailingly cheerful disposition, radiating an energetic and upbeat personality. Her core idol philosophy is encapsulated in the motto: "Smile!"

Following the abduction, Ruka participates with the Excellent Idols and protagonist Mimu Emilton in various comedic alien dimension competitions, including the Swing Ski, Muddy Quiz Contest, and Water-Scooter Fight. These events demonstrate her seamless integration into the group dynamic, with her individual contributions consistently reinforcing her role as a supportive and genial presence among the idols.

No expanded background beyond her participation in these interdimensional events and established personality traits is documented across other media.