Kaoru Orihara, nicknamed "Kaoru-no-Kimi" (Prince Kaoru) after the noble character in *The Tale of Genji*, is a 17-year-old first-year at Seiran Academy. Though one year older than Nanako Misonoo, she shares Nanako's class due to a prior year-long absence caused by undisclosed health issues, later revealed as breast cancer, which remains largely hidden from her classmates.

This nickname reflects her androgynous beauty and inherent leadership. She serves as class leader and basketball team captain, recognized for her athletic skill and tomboyish nature. Kaoru radiates intense vitality and a deep love for life, partly fueled by an underlying fear of mortality stemming from her illness.

She is one of the "Magnificent Three" alongside Rei Asaka and Fukiko Ichinomiya. Kaoru shares a profound bond with Rei, acting as her closest friend and frequently urging Rei to care for her health. She fiercely opposes Fukiko's Sorority, denouncing its manipulation of students and the cruelty Fukiko inflicts on Rei. Kaoru becomes Nanako's protector, supporting her during bullying and advocating against the Sorority's elitism, which exploits Nanako and restricts Rei's freedom.

Romantically, Kaoru had a relationship with Takehiko Henmi (later revealed as Nanako's stepbrother). She ended this relationship after undergoing a mastectomy due to her breast cancer treatment. Her story concludes differently across media:
- In the manga, she marries Takehiko, moves to Germany, but dies two years later.
- In the anime, she recovers from breast cancer, marries Takehiko, emigrates to Germany, and gives birth to a healthy son.

Kaoru's character arc highlights resilience against injustice and illness. Her initial private struggle evolves into public advocacy when she challenges the Sorority's corruption, culminating in petitions to the school board. Her journey embodies themes of loyalty, defiance against societal hierarchies, and the pursuit of authenticity amidst personal suffering.