Madoka Kaguya is the refined and academically accomplished third-year student council president at Mihoshi Middle School, celebrated locally as "The Moon of Mihoshi Town." Her distinguished family background includes a father in government service and a world-renowned pianist mother. Madoka herself holds national championship titles in piano, archery, flower arranging, and tea ceremonies. These achievements stem partly from striving to meet her father's high expectations, a pursuit that initially fostered significant stress and perfectionist tendencies.

In her civilian life, Madoka possesses gentle blue eyes and long, layered purple hair adorned with dark magenta ribbons. Her standard attire consists of a pearl blue blouse beneath an indigo dress featuring a crescent moon belt buckle, accessorized with a matching brooch. Seasonal adjustments see her in shorter sleeves during summer and a light grey turtleneck with boots in winter, sometimes complemented by a gray caplet.

Madoka's path changes when she encounters the alien Fuwa and witnesses Hikaru, Elena, and Lala transform into Pretty Cure to defend Fuwa from the Notraiders. Though initially inclined to report the aliens, aligning with her father's government role, the sight of Fuwa's vulnerability during an attack galvanizes Madoka's resolve to protect her. This determination activates her transformation into Cure Selene, the Pretty Cure of the Moon, heralded by the incantation: "Light up the night sky! The mystery behind the moonlight! Cure Selene!"

As Cure Selene, her hair thickens into lilac with gold-banded forelocks, and she wears a white headband featuring celestial motifs. Her deep purple Cure dress displays a Southern Cross design, layered with a pale blue translucent skirt, complemented by crescent moon earrings and boots decorated with snowflake-like patterns. Subsequent upgrades introduce her "Twinkle Style" with a tiara and elongated hair, plus zodiac-themed forms: Capricorn (magenta ombre hair, goat horns) and Sagittarius (ponytail, archery-themed attire).

Her signature attack, Selene Arrow, manifests a bow from a crescent moon generated by her Star Color Pendant. Upgraded variants utilize specific Star Princess Pens: Capricorn Selene Arrow forms a goat-head bow, Sagittarius Selene Arrow conjures a larger arrow, and Aquarius Selene Arrow produces water-based weaponry.

Madoka's character arc focuses on overcoming familial pressure. Early episodes depict her anxiety around her father, including scripted conversations and guilt over concealing her Pretty Cure identity. During a national archery tournament, her perfectionism sparks tension with competitor Nasu Yumika, ultimately teaching Madoka to value sportsmanship above victory. Through developing friendships—particularly with Elena and Lala, with whom she shares experiences of parental expectations—Madoka gradually asserts her independence, culminating in confronting her father about her life choices.

The series epilogue reveals her future as a space investigator, following her father's career path while maintaining her own autonomy.