Madoka Kaguya, a third-year student and president of Mihoshi Middle School's student council, carries the epithet "The Moon of Mihoshi Town" due to her ladylike demeanor. Born to a government official father and a world-renowned pianist mother, her distinguished lineage imposes immense pressure to excel. This drives her to secure national championships in piano, archery, flower arranging, and tea ceremonies while maintaining top academic standing. Initially, these expectations cause severe stress and indecision, though she gradually learns to manage societal demands and assert her choices through lived experiences and friendships.

Her civilian appearance presents gentle blue eyes and long, layered purple hair accented by dark magenta ribbons on each side. She favors a pearl blue long-sleeved blouse with indigo detailing, paired with an indigo dress featuring thin white vertical lines and secured by a dark indigo belt bearing a crescent moon buckle. Accessories include a dark magenta ribbon with a matching crescent moon brooch at her collar, strappy dark indigo Mary Jane shoes, and grey tube socks. Seasonal adaptations manifest as shorter sleeves in summer, while winter sees light grey turtlenecks combined with dark purple boots and tights, sometimes accessorized by a grey caplet.

Upon transforming into Cure Selene, the Pretty Cure of the Moon, her appearance shifts dramatically: her hair thickens into lilac, secured by a gold band on the forelocks beneath a white frilly headband adorned with blue and purple bows, a blue sphere, and a crescent moon. Her costume comprises a deep purple bodice emblazoned with a white Southern Cross, white puffy sleeves, and a purple skirt boasting elongated pleats tipped with yellow stars. She wears a purple choker with a light blue star, crescent moon earrings, and white-and-purple boots displaying pale blue snowflake patterns. In her enhanced "Twinkle Style," her hair lengthens with star embellishments, her headband evolves into a tiara, and her dress acquires light blue wraps and wing-like extensions. Zodiac-specific forms include Capricorn, distinguished by magenta goat horns and heart motifs, and Sagittarius, featuring a ponytail, archery-themed attire, and a golden bow-and-arrow weapon.

Her journey to becoming Cure Selene ignites upon encountering Fuwa, a celestial fairy, alongside alien visitors Lala and Prunce. Though initially feeling obligated to report extraterrestrial presence to her anti-alien government official father, Madoka hesitates after witnessing Fuwa's innocence. When the antagonistic Notraiders assault, Madoka shields Fuwa, demonstrating such fierce resolve that Fuwa gifts her a Star Color Pendant and Star Color Pen. Overcoming her reluctance to defy familial expectations, Madoka transforms into Cure Selene to protect Fuwa, declaring: "Light up the night sky! The mystery behind the moonlight! Cure Selene!" Her combat style prioritizes precision and evasion, notably maneuvering through enemy-conjured dust storms and deploying the long-range "Selene Arrow" technique.

Relationships profoundly shape her evolution. Her father, Kaguya Fuyuki, imposes exacting standards that initially strain their bond, compelling her to hide her Pretty Cure identity. She later confronts him decisively regarding her autonomy. Bonds with classmates Elena Amamiya (Cure Soleil) and Hagoromo Lala (Cure Milky) evolve from limited interaction into profound camaraderie, finding resonance with Lala's parallel familial pressures. These friendships empower her to embrace imperfection and self-determination.

Long-term development reveals her becoming a space investigator, following her father's professional footsteps while retaining her signature greeting, "Good day" (ごきげんよう). Her name embodies thematic significance: "Kaguya" references both archery (矢, "arrow") and the lunar princess from *The Tale of the Bamboo Cutter*, while "Madoka" (円, "round") alludes to the moon's phases. "Selene" derives from the Greek Titan goddess of the moon, cementing her celestial motif.