Hoshina Hikaru, a second-year middle school student in Mihoshi Town, possesses a deep fascination with constellations, space, and astronomy. Her naturally imaginative and curious spirit drives thorough investigations into topics that capture her interest, though this enthusiasm can sometimes surface as stubbornness or impulsive actions. While generally cheerful, she experiences moments of profound distress, especially following setbacks like losing the Taurus Princess Star Color Pen or her first solo defeat against Garuouga.

Her family heritage shapes her: her father passed down his passion for cryptids and space exploration, including his distinctive catchphrase, while her mother contributed artistic inclinations. Hikaru inherited her mother's pink hair and her artistic passion for drawing stars. Her grandfather Harukichi exhibits sternness about routines like morning greetings, contrasting with her grandmother Youko and mother Terumi, who actively encourage her adventurous spirit, often providing packed lunches for her explorations. An elderly friend, Sorami Ryoutarou, operates the local planetarium and gifted her the crucial notebook linked to Fuwa's emergence, showcasing Hikaru's capacity for intergenerational bonds.

Hikaru's extraordinary journey begins during stargazing; witnessing a shooting star while sketching constellations triggers a vision of a mouse-like alien. Connecting stars into a new constellation in her notebook causes it to glow, materializing the creature she later names Fuwa for its fluffy appearance. Fuwa's portal-creating ability accidentally transports them both into space, where Hikaru briefly glimpses a dark-shrouded heart-shaped planet before awakening. Initially dismissing it as a dream, she later confirms Fuwa's existence and pursues her, leading to encounters with extraterrestrial life.

While chasing Fuwa, Hikaru meets alien visitors Lala Hagoromo and Prunce after their spacecraft crashes. When the antagonistic Notraiders target Fuwa, Hikaru's fierce determination to protect the fledgling fairy manifests a Star Color Pen and Pendant, enabling her transformation into Cure Star. This form grants space survivability without Fuwa's aid and combat abilities, including star-platform generation for zero-gravity movement and the signature "Star Punch" attack. Subsequent encounters lead schoolmates Elena Amamiya and Madoka Kaguya to join as Cure Soleil and Cure Selene, forming the core Pretty Cure team. Later, the shapeshifting alien Yuni, previously the phantom thief Blue Cat, becomes Cure Cosmo after resolving her mission to save Planet Rainbow.

Throughout the interstellar mission to collect twelve scattered Princess Star Color Pens and revive the Star Princesses, Hikaru's leadership evolves. Early tendencies to disregard boundaries when excited mature into considerate supportiveness, notably encouraging Lala to reconcile with her family. Her relationships deepen: she idolizes Elena and Madoka as school role models, persistently befriends the initially aloof Yuni, and shares a uniquely close bond with Lala, symbolized by their asymmetrical Cure designs featuring single stockings on opposite legs. Her protective devotion to Fuwa remains central, culminating in profound grief when Fuwa sacrifices herself to save the team from Ophiuchus Star Princess (Darknest), subsequently losing her memories.

In the film *Star☆Twinkle Precure: These Feelings Within The Song of Stars*, Hikaru and Lala discover an extraterrestrial life-form fragment that reacts to Hikaru's excitement. Naming it Yuma, they nurture it while evading alien hunters. During a climactic battle, Hikaru and Lala sing the "Song of Shooting Stars" to calm Yuma's distress, facilitating its evolution into a new planet.

Fifteen years post-mission, Hikaru achieves her dream as an astronaut, sporting short bobbed hair with a white streak honoring Lala. On her inaugural space mission, Fuwa—having regained memories and powers—creates a portal transporting Hikaru's spacecraft to reunite her with Lala (now a planetary inspector) and Yuni (restored on Planet Rainbow).

Her design consistently reflects cosmic themes: civilian outfits feature star motifs in pink and blue dominated palettes, while her Cure Star form incorporates planetary elements like Saturn-shaped head ornaments and spherical twin-tail ends. Signature details include gold star accessories, a single star-patterned stocking, and feather-like sleeve elements. Her catchphrase "Twincool~☆" (originally "Kirayaba~☆") reflects inherited linguistic creativity from her father.