Sarah Bellum operates as Mayor Mayer's indispensable assistant in New Townsville (Tokyo City), managing a substantial share of his responsibilities. She functions as the operational intelligence behind city governance, prioritizing tasks and advising the mayor in crises. Her appearance features blonde hair and she typically conceals her face behind a tablet computer marked with lipstick impressions. She wears a dark red or sometimes white dress, gold bangles on each wrist, and black high-heeled shoes.

Fuzzy Lumpkins harbors an unrequited romantic interest in her, feelings she does not return and eventually comes to dislike. With the Powerpuff Girls Z, she acts as a mentor or elder-sister figure, offering calm guidance and practical advice during their missions. She consistently provides critical insights through her high intelligence and sharp situational awareness.

Sarah possesses no superhuman powers, relying instead on sharp political acumen, organizational skills, and quick decision-making to support the city. Her resilience shows during physical confrontations, as when she held her own against the superpowered Sedusa through tenacity and tactical thinking. However, her ordinary human physiology leaves her vulnerable to injury and fatigue, especially after prolonged struggles.

Her background includes attending elementary school with Professor Utonium and Miss Keane, indicating longstanding ties to key New Townsville figures. She maintains a professional yet reclusive personal life, prioritizing her career over social interactions or romance. Her character design and core role remain consistent throughout the anime series.