Kyoya Ootori, the third son of the wealthy Ootori family overseeing a healthcare zaibatsu, faces intense familial pressure to surpass his two older brothers. His goal is to win his father Yoshio Ootori's approval and potentially become patriarch, though succession traditions make this unlikely. This struggle defines his early motivation, driving him to "paint the perfect picture on a canvas already placed inside a magnificent frame."

As a second-year student at Ouran Academy, Kyoya co-founded the Host Club with Tamaki Suoh. While Tamaki is president, Kyoya operates as the club's indispensable strategist and manager, earning the title "The Shadow King" for his behind-the-scenes control. He meticulously handles finances, merchandise, event planning, and data tracking via notebooks or devices. His detailed dossiers on guests and students, coupled with sharp business sense, ensure the club's solvency despite Tamaki's extravagance.

Kyoya presents a façade of pragmatism, calculation, and detachment, frequently stating he acts only for tangible personal or familial benefit. He maintains a polite but aloof demeanor towards influential figures, initially viewing his friendship with Tamaki as a strategic network expansion. However, this mask hides genuine concern, revealed when he exposes an antique scam to protect a stranger or reprimands Haruhi Fujioka for confronting danger. Haruhi observes this contradiction, noting he acts "like a nice guy" despite his claims.

His relationship with Tamaki sparks significant growth. Initially seeing Tamaki as a tool, Kyoya's frustration with Tamaki's carefree nature culminates in an emotional confrontation where Tamaki challenges his resignation to familial limits. This breaks Kyoya's emotional restraint and forges a true bond. Through this friendship and the Host Club, Kyoya gradually values authentic connections over his obsession with surpassing his brothers, though his ambition persists. His father later acknowledges this development, especially after Kyoya anonymously thwarts a hostile takeover of the family business, signing it "K.O."

Kyoya exhibits low blood pressure, causing chronic fatigue and extreme irritability when awakened early, leading to nicknames like "Hypotensive Devil." He is often depicted adjusting his rimless glasses, emphasizing his analytical nature. His character design features short black hair and gray-brown eyes. Lavender is his signature Host Club rose color, symbolizing privilege in Japanese culture and enchantment in the West. He marries a partner chosen for familial benefit but reportedly develops love over time. Later, he resides in the United States for university studies and owns a cat named Noir.