Kuro Usa, also known as Kurousa, is a brown-furred rabbit from the magical world of Bunniesfield. Created by Sanrio in 2004, he forms one half of a twin pair with his brother Shirousa, a white-furred rabbit. Both share a May 26 birthday and work as professional pastry chefs in their homeland.

Kuro Usa displays a gentle, kind, and relaxed demeanor, frequently showing concern for Shirousa, who views himself as the duo's leader. His culinary focus centers on chocolate-based desserts, contrasting Shirousa's specialty in fruit and cream cakes. Their joint creations consistently delight customers. Physically, he has brown fur, pink inner ears, black eyes, a beige muzzle and belly, and distinctive eyebrows.

The twins' journey transports them from Bunniesfield to the human world, where they befriend a girl named Sophia. Initially hidden from society, they nurture Sophia’s baking talents despite her inexperience. Their existence eventually becomes public knowledge. Throughout these events, Kuro Usa shares the recurring catchphrase "Kitto umaku iku yo" (We’ll surely succeed) with Shirousa. After integrating into human society, they expand their activities to broader community contributions.