Kuguru Uki attends sixth-year elementary at Aibo Academy, a classmate of Gao Mikado and childhood friend Baku Omori. Her distinctive hair features two small pigtails protruding from circular lamps capable of lighting up, complemented by red-framed glasses. She typically wears a white long-sleeved sailor-style shirt with a fuchsia ribbon and teal accents extending into a skirt, paired with thigh-high white boots matching the teal trim.

Renowned as "The Library" for her vast Buddyfight card knowledge, Kuguru frequently uses a tablet to display card data during analyses. She demonstrates strong loyalty and protectiveness toward her friends, evidenced by blackmailing Baku into building Gao's deck and physically intervening when Baku dismisses emotional sentiments. She harbors a recurring crush on Baku, hugging him after Gao's victories and reacting visibly to his comments about prioritizing food over relationships. Kuguru also carries cat toys and shows affection toward feline Buddy monsters like Cait Sith.

As the non-combatant analyst and strategist for Team Balle du Soleil, she provides tactical support during matches and emotional encouragement to teammates Gao, Baku, Kiri Hyōryū, and Tetsuya Kurodake. Her contributions include crucial deck-building assistance and situational advice. Her documented fight record includes a win against Baku (disguised as Shusui Kanahebi) and a loss to Zanya Kisaragi.

Her role diminishes in later seasons like *Hundred* and *X*, where narrative focus shifts; she appears sporadically, maintaining her supportive function without significant development or expanded backstory in spin-offs or movies. A cameo features her with friends on a television screen in *Cardfight!! Vanguard Movie: Neon Messiah*.