"Shimajirō to Niji no Oasis" is a children's anime series that centers on the adventures of Shimajirō, a cheerful and curious young tiger, and his friends as they explore a magical world filled with wonder and learning. The story begins when Shimajirō discovers a mysterious oasis hidden within a rainbow. This oasis, known as the Rainbow Oasis, serves as a gateway to a vibrant and fantastical realm where the laws of nature are slightly different, allowing for extraordinary experiences and encounters.

In this magical oasis, Shimajirō and his companions—including his sister, Mimi, and his friends, Torippī the bird and Nyanmi the cat—embark on various adventures. Each episode typically involves a new discovery or challenge, often tied to themes of friendship, problem-solving, and personal growth. The characters frequently interact with whimsical inhabitants of the oasis, such as talking plants, animals, and other fantastical creatures, who help them learn valuable lessons about cooperation, kindness, and curiosity.

The narrative structure is episodic, with each installment presenting a self-contained story that contributes to the overarching theme of exploration and learning. The Rainbow Oasis itself is a central element, serving as both a setting and a metaphor for the boundless possibilities of imagination and discovery. Through their adventures, Shimajirō and his friends encounter situations that encourage them to think creatively, work together, and appreciate the beauty of the world around them.

The series is designed to be educational and entertaining for young audiences, blending lighthearted humor with gentle moral lessons. The characters' interactions and the challenges they face are crafted to resonate with children, emphasizing the importance of empathy, perseverance, and the joy of learning. The simplicity of the plotlines and the colorful, imaginative world of the oasis make the series accessible and engaging for its target demographic.