Miu Fuurinji descends from a distinguished lineage of martial artists, the granddaughter of Hayato Fuurinji and daughter of Saiga Fuurinji and Shizuha Fuurinji. Her heritage blends the physical superiority of both the Fuurinji Clan and the Kuremisago Clan. After her mother's death during her infancy and her father's subsequent absence, Hayato Fuurinji raised her alone. Her childhood involved constant global travel and rigorous martial arts training under his guidance, leaving little opportunity for social development or friendships. A significant encounter occurred at age six when she inspired Kenichi Shirahama and his friend Ryuto after they witnessed her defeat local thugs. During this meeting, she exchanged her Yin Yang badge for Kenichi's cat badge, an item she treasured.

Physically, Miu possesses fair skin, bright blue eyes, and waist-length blonde hair with a distinctive beauty mark under her left eye. She is of average height with a slender yet athletically defined build, featuring pronounced curves including a well-endowed bust, slim waist, and flared hips. Initially at school, she wore non-corrective glasses and braided her hair to appear plainer and avoid peer jealousy stemming from her looks, academic prowess, and athletic abilities. After an encounter with Chikage Kushinada accusing her of lacking authenticity, she abandoned this facade and embraced her natural appearance. Her typical attire includes a purple spandex outfit for training and daily home activities, often covered by casual wear like sweaters or a yellow apron. She consistently wears two red hairclips gifted by her mother—one concealing a small blade and the other a lockpick. During her brainwashing as "Bulu," her appearance shifted to include unruly hair, emotionless eyes, and a traditional Tidat outfit: a light blue one-piece garment, leg guards, a hat, and a bird mask.

Miu exhibits a cheerful, kind-hearted, and upbeat personality despite her challenging upbringing. She manages most household chores and finances, displaying fierce concern over monetary issues, sometimes perceived as greediness—such as urging Kenichi to sell combat medals or confiscating an opponent's gold shoes as "spoils of war." Childhood isolation caused social ineptitude, leading to initial nervousness in friendships. She deeply cherishes her relationships, particularly with Kenichi, and becomes distressed if friends seem upset. Naivety surfaces in her childlike enthusiasm for new experiences like aquariums or merry-go-rounds, reflecting missed childhood opportunities. She adores cats, frequently playing with them or interacting affectionately with cat-like individuals. However, when enraged—especially if friends are harmed—she enters an uncontrollable berserker state requiring physical intervention to regain composure. This "other personality," linked to her Dou-type fighting style, frightens her due to the risk of harming others.

Her combat abilities are prodigious, nearing expert-level mastery. Trained from infancy in the Fuurinji Style, she incorporates techniques from multiple Ryozanpaku disciplines, making her a hybrid martial artist. Her fighting emphasizes agility, acrobatics, and high-speed kicks, with reflexes so honed she instinctively throws anyone approaching from behind. Key techniques include the aerial Fuurinji Benikawasemi (a head-targeting cross kick), Fuurinji Kouhou Yoku (a drill-like spinning kick), and Fuurinji Mist Falcon (a neck-snapping leg throw). Defensively, she employs Seikūken (a calm-mind barrier) and its advanced form Ryūsei Seikūken, which predicts and counters attacks by reading an opponent's flow. Her sensory skill Rittoku No Kan heightens perception, reducing reaction time to one-tenth normal. After brainwashing by Silcardo Jenazard, she learned Pencak Silat, adding weapon basics and techniques like the Juls Combo (vital-point strikes) and Topan Kait (inverted kicks). She also possesses espionage skills, including lock-picking and bomb disposal, from her travels with Hayato. Though initially unmatched among peers, YOMI disciples later challenged her dominance.

Her character arc involves significant emotional growth. A lifelong quest to uncover her parents' identities drives much of her development; she nearly joined Yami for answers before learning her father was framed for her mother's murder. After reconciling with him, she finds peace. Romantically, she evolves from obliviousness to Kenichi's feelings to overt devotion. Early signs include jealousy of other girls, relief when he rejects Renka's invitation to China, and blushing at his affectionate words. After he saves her during a ski trip, she becomes physically affectionate, hugging him tearfully when he returns from dangerous missions. She eventually kisses his cheek, acknowledges her love, and states she would die for him. Post-series, she marries Kenichi, adopts the name Miu Shirahama, and they have a daughter.