Centorea Shianus, often called Cerea by those closest to her, is a centaur and the third non-human resident to join the Kurusu household. Her background is rooted in a noble family of knights, having received intense martial and chivalric training from a young age, which shaped her honest, earnest, and somewhat rigid personality. A significant facet of her background is that she is a half-blood; her father was a human and her mother a centaur, a fact she was unaware of until her mother revealed it to her.

Described as incredibly honorable and chivalrous, Centorea carries herself with the formal bearing and archaic speech patterns of a medieval knight. She possesses a strong moral code and often acts as the voice of reason and the straight man among her housemates, attempting to keep order and lead by example, though her strict tone can sometimes make it difficult for others to follow her. Despite her stoic and composed exterior, she harbors a girlish and romantic side, complete with fantasies of heroic scenarios. This leads to her becoming easily flustered, deeply embarrassed, or awkwardly shy when faced with romance, intimacy, or teasing, especially from the other girls.

Her primary motivation and central role in the story are defined by her relationship with Kimihito Kurusu, whom she affectionately refers to as Master. She met Kimihito while chasing a purse-snatcher, believing that a dramatic, fateful encounter would lead her to a worthy master due to her literal interpretation of manga tropes. After Kimihito risked his safety to protect her, she vowed him her lifelong loyalty and moved into his home as part of the interspecies exchange program. She sees her duty as his knight and protector above all else, which often puts her in a leadership role among the other monster girls, including Miia, Papi, Suu, Meroune, and Rachnera. Her relationships with her housemates are complex; she has a friendly rivalry with Miia, a deep respect for Mero, and a cautious, often resentful, tolerance of Rachnera's lascivious behavior, though she ultimately comes to care for them all as family.

Throughout the story, Centorea shows development by learning to balance her rigid sense of duty with her personal feelings and the chaotic reality of daily life. She learns to show humility, loosen her strict adherence to tradition, and gradually becomes more accepting of her own romantic and even slightly permissive desires for intimacy with Kimihito. Her willpower is notably strong, allowing her to briefly resist the instinctual effects of a full moon, though she is ironically very susceptible to hypnosis.

As a centaur, Centorea possesses remarkable physical abilities. Her maximum running speed is sixty kilometers per hour, and she demonstrates exceptional physical strength, capable of lifting two other large monster girls simultaneously or knocking out a wild boar with a single strike. She is a highly skilled swordswoman who can wield a large claymore with one hand, a master jouster who once dueled her undefeated mother to a draw, and a proficient archer. Due to legal restrictions in human society, she typically uses a mock sword. Her physiology also dictates that she is strictly herbivorous, unable to eat meat, fish, or eggs, and her sense of taste is sharper than a human's. She has a well-known but embarrassing fondness for carrots.