Chibimaru-chan, called Penelope in English releases, is an infant hamster instantly recognizable by the distinctive yellow blanket perpetually worn over her head. She lives with her owner, Kylie as the youngest Ham-Ham. Her communication consists solely of sounds like "Ukyu!" in Japanese or "Ookwee" and "Ookyoo" in English, understood by few characters—primarily Pashmina.

Chibimaru-chan shares a deeply attached, sister-like bond with Pashmina, her main caretaker and emotional anchor. This central relationship defines her; separation during babysitting, seen in episodes such as "Watching Over Cute Penelope" and "Knitting Barrette," triggers visible distress and jealousy. Her childlike perspective sometimes misinterprets Pashmina’s actions, as in "Penelope’s Dream."

Exhibiting age-appropriate innocence and naivety, Chibimaru-chan often experiences mishaps. Beyond Pashmina, she forms meaningful friendships, notably with Marron during "Marron’s Autumn Festival." Here, she aids Marron emotionally and helps prevent a flood, with Marron comprehending her unique speech. Their similar size and physical resemblance—visible when Chibimaru-chan lacks her blanket—reinforce their camaraderie.

Though rarely shown without her signature blanket, brief glimpses reveal her natural brown-and-white coloration. These occur in media like the English dub's opening, the game *Hamtaro: Ham-Hams Unite!*, and various merchandise.

Her background includes shifting familial connections across adaptations. Early material like *Tottoko Hamutaro: Hamuchanzu de Gozaimachu! Vol.1* identifies her as Bijou’s younger sister. Later works, including the anime, emphasize her sisterly dynamic with Pashmina without confirming biological ties.

Chibimaru-chan’s narrative explores nascent affections extending beyond hamsters—toward Herbert the pig, Kylie’s human cousin Ethan, and a rabbit encountered at Ethan’s school in season three. These experiences reflect her growing social curiosity while preserving her childlike essence.