Hikaru Hoshina is the main protagonist and leader of the Star Twinkle Pretty Cure team, who transforms into the legendary warrior Cure Star. She is thirteen years old and a second-year student at Mihoshi Middle School. Her birthday falls on April 12th, a date that aligns with her love for space as it marks the International Day of Human Space Flight. Hikaru lives with her mother, who works as a manga artist, and her grandparents. Her father is frequently away on business trips, traveling the world to research unidentified mysterious animals. This upbringing, coupled with her father's passion for cryptids and space, has a profound influence on her, as she inherits his signature catchphrase and her intense curiosity about the cosmos. She also shares her mother's artistic inclinations and is quite skilled at drawing.

Hikaru is defined by her overwhelming curiosity, vivid imagination, and boundless energy. As a Genki Girl, she approaches life with an excitable and enthusiastic demeanor, especially when anything related to constellations, aliens, or the universe is involved. Her defining trait is being a xenophile; she has a deep and genuine fascination with all things extraterrestrial, often gushing with excitement at the sight of a new alien species or planet rather than showing fear. This impulsive and intuitive nature means she is a person of action, often following her gut feelings before thinking things through. While this makes her a brave and determined individual, it can also lead to her being stubborn and occasionally inconsiderate. Her lack of patience and tendency to act rashly sometimes cause friction with her more logical teammates. However, she is never malicious. At her core, Hikaru is a kind-hearted and caring person who deeply values her friends. She has a strong protective instinct, particularly for the fairy Fuwa, and her desire to protect those she cares about is a primary motivator for her actions.

Hikaru's journey begins when she draws a new constellation in her notebook, which magically brings the fairy Fuwa to life. She soon encounters the alien Lala Hagoromo and the creature Prunce, who are searching for legendary warriors called Pretty Cure. When the villainous Notraiders attack to capture Fuwa, Hikaru's fierce determination to protect her new friend awakens her powers, allowing her to transform into Cure Star. As Cure Star, she serves as the heart of the team. Her role is not just as a fighter, but as the emotional core who unites her diverse group of friends. She is the one who often pushes the team forward with her enthusiasm and helps her teammates overcome their personal struggles with her straightforward and insightful encouragement.

Her key relationships are central to the story. Her bond with Lala is particularly important, as the two start as opposites with Hikaru's impulsiveness clashing against Lala's analytical mind. Through their adventures, they learn to understand and complement each other, with Hikaru helping Lala embrace her emotions and courage. She is also fiercely protective of Fuwa, viewing her almost like a child or a younger sister. Her relationships with Elena Amamiya and Madoka Kaguya, her other teammates, are built on mutual respect, and she often looks out for their well-being. Despite being good-natured and friendly, it is noted that as a child, Hikaru preferred to play alone and was somewhat self-centered, making the strong friendships she develops over the course of the series a significant personal achievement.

Throughout the series, Hikaru experiences clear personal growth. She learns to be more considerate of her friends' feelings and to balance her impulsive nature with patience. A major part of her development is her struggle to unlock her full potential, which requires her to confront her own doubts and weaknesses. The story culminates with her facing the possible loss of Fuwa, which deeply affects her. In the epilogue, set years after the main events, Hikaru achieves her lifelong dream of becoming an astronaut. Her appearance changes to reflect her maturity, as she cuts her signature pigtails into a shorter bob with a turquoise streak, a nod to her friend Lala. The series ends with her fulfilling a promise to reunite with Lala and Fuwa in space.

As Cure Star, Hikaru's abilities are themed around stars and constellations. Her signature attack is Star Punch, a powerful melee strike where she launches a star-shaped burst of energy at her opponent. She is also a defensive fighter, capable of summoning Star Shields to block attacks. By using the Princess Star Color Pens, she can alter the color and properties of her Star Punch to match the zodiac sign of the pen, such as Taurus or Pisces. Her transformation and fighting style are visually distinctive, with Cure Star's costume featuring floating rings on her pigtails that resemble small planets and a fashionable asymmetric design.