Kapuru-kun, called Kaburu-kun in Japanese media, is a young hamster with a white and brown coat who consistently wears a distinctive green swimming cap. He occasionally replaces this cap with other head coverings, like a giant red saucepan for hiding or a seashell during beach visits. His passion for hats drives his constant hunt for new objects to wear atop his head.

Shy and hesitant by nature, Kapuru-kun still exhibits persistent curiosity for unconventional headwear. He lives with human owners Kip and Sue, appreciating his home but expressing discomfort with excessive pampering. Among fellow hamsters, he admires Boss as a model of independence due to Boss's field-hamster background.

His closest bond is a playful, energetic friendship with Stucky, often centered on games like hide-and-seek. During *Hamtaro: Ham-Ham Heartbreak*, antagonist Spat steals Seedric’s acorn hat and gifts it to Kapuru-kun. Though initially reluctant to return it despite Hamtaro’s urging, Kapuru-kun reconsiders after empathizing with Seedric’s loss. He personally returns the hat, forging a connection with Seedric over their shared enthusiasm for headwear.

Kapuru-kun rarely removes his green cap, doing so only when fanning an ill Laura or swapping it for a seashell at the beach. Officially listed as 7.7 cm tall, he is sometimes portrayed shorter than most hamsters except Penelope. His Japanese name "Kaburu" directly references his hat-centric trait, meaning "to put something on one’s head." Kapuru-kun shares Hamtaro’s birthday of August 6th, established in a special episode.