Shimajiro Shimano is a young yellow tiger boy living on Challenge Island. As the eldest child in the Shimano family, his younger sister is Hana. His father, Shimataro, works as a mailman and struggles with tasks like cooking. His mother, Sakura, handles household duties and disciplines the children when needed.

Shimajiro bubbles with curiosity and cheerfulness, though he can sometimes be stubborn or selfish. Daily adventures bring life lessons, often resolving conflicts after facing consequences. He dreams of becoming a soccer player or entomologist, fueled by his passion for soccer, dinosaurs, and insects, along with a love for donuts. Yet thunderstorms, ghost stories, and eating green peppers unsettle him.

His world centers on preschool and kindergarten life alongside friends like the rabbit Mimirin, the parrot Torippi, and the lamb Ramurin. After Ramurin leaves Challenge Island, he befriends Nikki, a pink cat. Their cooperative adventures and occasional conflicts teach him responsibility, empathy, and problem-solving. He shows protectiveness toward Hana, though sibling disputes arise, like the time he cross-dressed to humor her wish for an older sister, leading to comedic trouble.

Notable experiences include toilet training aided by anthropomorphic elements. His curiosity sometimes lands him in trouble, whether overestimating his abilities or daydreaming during chores. Still, he consistently offers loyalty and support to friends and family facing challenges.

Across all media—TV series, OVAs like "Shimajiro's Traffic Safety" and "Shimajiro's Fire Brigade," and films like "Shimajiro and the Pirate Ship"—Shimajiro explores his surroundings, learns social norms, and confronts fears. His growth unfolds through recurring moments: making amends after arguments, helping those in need, and maturing while keeping his innate curiosity alive.