Kimiko Ayanokouji is a student at Seika Girls Academy and one of Japan's wealthiest individuals, her family's fortune equating to the nation's GNP. She has violet hair, grey eyes, stands 1.62 meters tall, weighs 47 kilograms, with body measurements of 85-58-88, blood type AB, and a birthday on August 31st.

She leads a group of five affluent girls and is the fraternal twin sister of Miyuki Ayanokouji. With a reported IQ of 200, Kimiko also claims a special talent for ESP, an ability her sister dismisses as fabrication. Her character is aloof, narcissistic, and prissy; she revels in her immense wealth, considers herself profoundly beautiful, and expects to be treated like royalty.

Kimiko secretly masterminded an attack on her own group by hiring criminals to assault the school, orchestrating the event for personal excitement. She later avoided consequences by bribing the principal with 100 billion yen for repairs. Her conduct includes manipulating the police assigned for her protection, attempting to seduce an adult detective despite her youth, and diverting her friends during critical situations, actions which nearly resulted in casualties.

Her relationship with her twin sister Miyuki is strained, marked by Miyuki's frequent exasperation with Kimiko's antics and open criticism of her reckless behavior.