Kaoru Matsubara, alias Powered Buttercup, is a 13-year-old athletic student and her team’s foremost physical powerhouse. Her spiky black hair, sharp green eyes, and sporty wardrobe—baggy shorts, sneakers, and unisex jackets—underscore her tomboy identity. Though initially self-conscious about the short skirt in her green superhero suit, she grows to tolerate it, accessorizing with black fingerless gloves and green hair clips during missions.

Daughter of retired wrestler Tokio Matsubara and homemaker Mitsuko, Kaoru competes fiercely with her brothers Dai and Shou, whose teasing cemented her rejection of overt femininity. Childhood soccer practice with gifted cleats honed her athleticism, later expanding to martial arts and tennis. While schoolmates admire her skills, she dodges fangirl adoration with gritted teeth.

Her blunt, sarcastic edge softens through teamwork with peers Momoko and Miyako, whom she initially dismissed for their girlishness. Despite snark, Kaoru fiercely defends allies and family—a loyalty villains manipulate. Growth tempers her brashness, allowing camaraderie and subtle acceptance of feminine traits without erasing her dry wit or fiery temper.

Wielding a Daruma Otoshi hammer that launches energy blasts or elongates for ranged strikes, she dominates close combat with moves like "Megaton Dunk" and "Buttercup Finish." Though capable of devastation, she spares vulnerable foes. Her belt buckle’s energy core activates via the phrase "Powered Buttercup," fueling her strength.

Pivotal moments include embracing her skirt-clad alter ego, seeking her mother’s counsel during doubts, and hiding a secret fear of ghosts. Her design nods to Akane Tendo’s spiritedness and Goku’s spiky hair, while her name—omitting the traditional "ko"—reflects her defiance of gendered norms.