Originally named Peach in Japanese, Pucci is a robotic dog companion created by Professor Utonium for his son Ken. During a Chemical X experiment, Pucci accidentally dropped a daifuku into the substance, transforming it into Chemical Z. When Ken later fired Chemical Z at an iceberg threatening Tokyo Bay, the blast released black and white Z-rays across the city. Absorbing a white Z-ray granted Pucci sentience, human-like speech, enhanced cognitive functions, and a sixth sense to detect monsters or individuals affected by the black Z-rays – though strong scents like cosmetics can mask this ability.

Transformed by this event, Pucci serves as the primary communicator and coordinator for the Powerpuff Girls Z team. His bark activates their transformations and replenishes their depleted powers. Functioning as a living alert system, he uses his enhanced senses to identify emerging city-wide threats and relays critical information to both the team and Professor Utonium. Pucci shares a unique connection with the three main heroines, as all were impacted by the white Z-rays during the initial incident.

His existence remains intrinsically tied to the ongoing conflict stemming from his accidental modification of Chemical X and the resulting Z-ray dispersal. Pucci operates consistently as a constant companion to Ken and assists the team from their base throughout the series.