Cateau hails from the Flower Star, a realm of plant spirits and fairy-like beings. The king of the Flower Star dispatches him as one of two messengers to Earth, tasked with finding a descendant able to locate the magical seven-colored flower, a symbol of the royal family's authority. On Earth, Cateau appears as a talking cat. Together with his companion Nouveau, a talking dog, he identifies Lunlun Flower in France as the sought descendant due to her heritage linked to the Flower Star people through her late mother. On her 15th birthday, Cateau and Nouveau recruit Lunlun for the quest to find the seven-colored flower.

Throughout their journey across Europe and Northern Africa, Cateau acts as Lunlun's guardian and advisor. He assists her by sensing dangers and navigating obstacles, particularly those posed by the antagonists Togenishia and Yabouki who seek to steal the flower. Cateau's primary function is supporting Lunlun's mission, helping those they encounter, and safeguarding her from harm. He remains her constant companion, contributing to problem-solving and offering guidance during their travels. His presence underscores the theme of loyalty and protection central to the quest.

In official media, including the main 50-episode series, Cateau's role is consistently that of Lunlun's companion. The theatrical short film "Hello Cherry Country" features the core cast.