Milk Usagi-chan, also called Rebecca Periwinkle, is a white rabbit member of the Milk Rabbit family. Originally the second oldest child, she became third after the retcon introduction of her older sister Catherine. Rebecca displays gentle forgiveness toward friends yet encounters occasional difficulties in peer leadership roles. She exhibits strong determination in pursuing goals and supporting others.

Rebecca nurtures a recurring princess aspiration, chronicling royal fantasies in a secret notebook. She rehearses princess mannerisms like dancing and curtseying for her baby brother. Intelligent and quick to trust others' good intentions, this trait sometimes leads to deception, such as when believing Buster Slydale’s false pledge to cease trickery.

Family life highlights her parents' focus on nurturing bonds; shared dinners with younger brother Oliver are common. Father Alex Periwinkle serves as the village doctor, while mother Kate Periwinkle works as the village nurse. Kate fosters imagination by telling fairy tales of princesses and fairies to the children.

Rebecca's media prominence has shifted across the franchise. She starred as the central heroine in the 2007 OVAs, embodying leadership and emotional warmth among friends. Around 2010, franchise focus transitioned to the Chocolate Rabbit family, particularly Freya Chocolate. By 2017, Rebecca’s role reduced to recurring appearances, and in one musical ballet advertisement, she appeared only as a background dancer while Freya held the lead. This represented a narrative demotion from her prior status.

Her design includes removable floral-patterned dresses. Figures of her and her family feature movable limbs for posing. The family received redesigned outfits in Japan’s 2022 re-releases.