Kiki Seiran is a noblewoman and a knight who serves as one of the two closest aides to Prince Zen Wistaria of the kingdom of Clarines. As the sole heir to Earl Seiran, the head of one of the kingdom's oldest and most powerful noble families, she is set to inherit her father's estate and become one of the youngest lords in Clarines upon his retirement.

Physically, Kiki is a young woman of medium height, standing at 165 cm, with honey-blonde hair and blue-grey eyes, though the anime adaptation gives her violet eyes. She typically wears her hair in a low ponytail, but later cuts it short as an expression of her personal resolve. Her attire is practical and formal, usually consisting of a sleeveless black top, purple outer garments with gold embellishments, and arm guards that accommodate her sword. She generally avoids wearing dresses because they restrict her ability to carry a weapon, though she eventually learns to conceal blades within them and accepts formal wear for ceremonial occasions.

Kiki is renowned for her stoic and reserved personality, a trait she inherited from her late mother who passed away before Kiki turned five. She rarely displays overt emotion, maintaining a calm and composed demeanor even in tense situations. Her father has noted that her cold voice is very much like her mother's. Despite her outwardly disinterested expression, she possesses a dry, deadpan wit and delivers humorous remarks with a straight face, often causing a delayed reaction from those around her. She is fiercely independent and self-reliant, having kept to herself during her youth and preferring not to rely on others. However, she gradually opens up to a select circle that includes Prince Zen, her fellow aide Mitsuhide Rouen, the former assassin Obi, and the herbalist Shirayuki.

Her history includes studying swordsmanship at the Sereg Knight Circle, where she first met Zen. Her first encounter with Mitsuhide occurred at a ball, where both were hiding from other guests in an alcove. She chose not to give him her name at that time because she wanted to be recognized for her skill as a swordswoman rather than her noble status. When they met again later, Mitsuhide mistook her for a young man due to her short hair and sword, even inviting her to bathe with the other male trainees. She served as Zen's aide for over five years before Shirayuki entered their lives, having made an agreement with Zen that her service would last only six years before she would return home to assume her duties as the Seiran heir. This arrangement was kept secret from Mitsuhide, leading to conflict when he discovered it, though they resolved their differences through a duel. Mitsuhide subsequently asked her to extend her service to support Zen and Shirayuki, and after confronting her initially resistant father, she successfully negotiated a longer stay at the castle. She marked this decision by cutting off her ponytail.

Kiki's role in the story is that of a protector and trusted advisor to Prince Zen. Alongside Mitsuhide and later Obi, she forms a formidable trio dedicated to ensuring Zen's safety and supporting his goals. She is also a supportive presence for Shirayuki, respecting the herbalist's determination and independence. As the only two young women in their close friend circle, Kiki and Shirayuki often share rooms during travel and bond over personal matters, with Shirayuki enjoying the rare occasions when Kiki does her hair. Kiki initially harbored wariness toward Obi due to his past as an assassin, but she warmed to him after he demonstrated genuine loyalty to Zen, and the two developed a friendship marked by mutual teasing.

Regarding romantic relationships, Kiki has demonstrated significant personal growth and autonomy. She developed romantic feelings for her long-time partner Mitsuhide and resolved to propose to him when the time was right. However, when she finally proposed, Mitsuhide declined because his extreme loyalty to Zen meant he had never considered marrying anyone, wishing to remain by the prince's side indefinitely. Kiki accepted this decision without resentment, and they continued as close friends and partners. She later became engaged to Hisame Lugis, a childhood suitor. Their relationship initially formed as a temporary political arrangement during the Bergatt incident to draw out attackers targeting Kiki's potential suitors. After her proposal to Mitsuhide was refused, she reaffirmed her engagement with Hisame. Their dynamic is characterized by layered conversations filled with double entendres, sarcasm, and blunt honesty, creating an intellectual rapport that contrasts sharply with the more direct and prosaic communication style she shared with Mitsuhide. Kiki has stated that she and Hisame are well suited to each other.

Kiki is an exceptionally skilled swordswoman and a member of the Royal Guard. Her combat abilities are such that her movements are perfectly synchronized with Mitsuhide's when they fight together, making them an extraordinarily effective duo. Settling a duel between them is said to be particularly difficult, often ending in a tie. She wields a sword with a dark blue sheath and a hilt adorned with an aquamarine jewel. Her strategic prowess and combat skills are employed primarily to protect Zen and, by extension, Shirayuki. Her refusal to conform to traditional expectations of noblewomen, particularly her resistance to arranged marriages and her dedication to martial training and service, defines her character as someone who forges her own path while balancing duty to her family, her prince, and herself.