Kaoru Seta serves as guitarist for the band Hello, Happy World! while attending Yotsuba Women's University's Faculty of Arts - Theatre Department, Acting Program as a first-year student. She previously studied at Haneoka Girls' Academy, where she ranked among the most popular students. Standing 170 cm tall, she possesses angular facial features, crimson eyes, and long purple hair typically secured in a ponytail. Her style blends formal and boyish elements, consistently featuring high-collared shirts, vests, and pearl necklaces, with seasonal adaptations like sweaters in winter or floral-patterned shirts in summer.

Kaoru's defining theatrical "prince" persona permeates her interactions. She liberally employs Shakespearean or philosophical language—sometimes misapplied or misunderstood—and addresses other girls as "princesses" or "little kittens," a term carrying noted connotations in Japanese queer culture. This flirtatious demeanor fuels her popularity, particularly eliciting blushes from figures like Himari Uehara and Rimi Ushigome. Despite her performative confidence, she displays airheaded tendencies, such as misidentifying philosopher Friedrich Nietzsche's gender or wrestling with simple tasks like pushing a pull door. Her signature catchphrase "fleeting" (儚い *hakanai*) surfaces prolifically yet vaguely.

Her childhood contrasts sharply with this flamboyance. Once shy and plagued by low self-esteem, she was haunted by her failure to intervene when childhood friend Chisato Shirasagi faced bullying. This experience ignited her desire to emulate Chisato’s strength, leading her to theater in middle school. There, she deliberately crafted her princely identity as a transformative shield. Though initially perceived as a façade, Kaoru asserts this persona evolved into an authentic facet of her being, refined through acting and embraced as her true self. Her motivations intertwine atonement for past cowardice with preventing similar suffering in others, fueling people-pleasing behaviors. She meticulously fulfills fan requests, regardless of demand, and channels acting to express emotions like gratitude.

Relationships anchor Kaoru's narrative. Her dynamic with Chisato remains layered; Chisato knows her pre-persona self, uses the childhood nickname "Kao-chan" (which flusters Kaoru), and occasionally glimpses her private vulnerability. Within Hello, Happy World!, she supports band activities despite concealed fears—acrophobia and horror aversion—by immersing herself in character during performances. She exhibits emotional intelligence, deciphering Kokoro Tsurumaki's motives ahead of peers and soothing Saaya Yamabuki's nerves through humor. Bandmates cherish her reliability, though her reluctance to decline requests underscores her pushover nature.

Her interests span reading philosophy, equestrian pursuits (favoring fencing and horseback riding, skills honed via her uncle's horses), and hosting segments like "Shakespeare with Seta Kaoru" in high school and "Seta Kaoru's Masterpiece Theater" on Hello, Happy World!'s streaming channel. She professes enjoyment of sophisticated consumables—grape juice, Sachertorte, Vichyssoise—for their "cool" image but genuinely prefers simple fare like miso soup with rice cakes. She disdains raw seafood and battles morning sluggishness.

Kaoru's evolution traces from self-loathing bystander to assured performer who embraces her identity. Key milestones include reconciling past cowardice through theater, affirming her persona's authenticity despite Chisato's initial skepticism, and consistently leveraging acting to uplift others. Her journey underscores themes of self-acceptance and intentional identity construction, balancing flamboyance with introspection and quiet kindness.