In the world of the cheerful little Maruko, the chaos of her life and thoughts turns into innocent adventures alongside her kind-hearted grandfather. A moment of great joy quickly shifts into exaggerated fear of a luxurious dish that holds a dangerous secret. And while she dreams of being helpful to others, her enthusiasm fades quickly with her first setbacks, until her curiosity leads her to discover a mysterious box in her home. Its secret grows in her imagination day by day, transforming the simplest details of her small world into stories filled with fun and excitement.