Kyouya Sata is a central character introduced as a strikingly handsome high school student with long, messy blonde hair and red eyes. He cultivates a polite, charming "princely" public image at school, masking a colder, manipulative private personality prone to sadistic control over others. This stems from deep-seated trust issues rooted in childhood trauma: his parents divorced when their demanding work eroded their relationship, symbolized for him by a collapsing snowman he later learned his sister destroyed. After the divorce, he lived primarily with his workaholic father, often alone, rarely visiting his mother in Kobe until later.

Physically standing 178 cm tall, he is often noted for fashionable casual attire, mistaken for a model. His school uniform is a white blouse, gray cardigan, and striped red-and-white tie. Later, after marriage, his hair becomes shorter and less messy. Beyond his aloof exterior lie specific vulnerabilities: he avoids pets due to trauma from his dog's death in middle school, dislikes airplanes, expresses aversion to holidays like Christmas and Valentine's Day, and dislikes sweet foods. He requires corrective lenses for nearsightedness but typically wears contacts.

His relationship with Erika Shinohara defines his character progression. After she secretly photographs him to present as her fake boyfriend, he agrees under the condition she acts as his subservient "pet dog." Initially cruel and controlling—insulting her, breaking her phone, demanding obedience—his behavior shifts as genuine feelings develop. Key moments include punching a classmate who degraded her, covertly protecting her during a manipulative "date," and gifting her a heart-shaped necklace symbolizing possession that she treasures. He exhibits consistent jealousy over her interactions with other males, like Yuu Kusakabe or coworker Terasaki, but his emotional barriers gradually lower. He struggles to articulate affection, eventually whispering "I love you" during her birthday after intense effort.

His development intensifies through confrontations. When faced by Nozomi Kamiya—a playboy who sees Kyouya's former self—he rejects shallow relationships, admitting he once shared that mindset but changed due to Erika. Family interactions reveal more layers: his older sister Reika shares his sharp personality, and though initially distant from his mother, he reconciles after visiting with Erika.

By the story's conclusion, spanning years after high school, he marries Erika, becomes a father to their daughter Yuina, and demonstrates enduring commitment, completing his evolution from an isolated, cynical figure to someone capable of sustained familial bonds.