Miyuki Hoshizora, known as Emily in the English adaptation Glitter Force, is the main protagonist of the series. She is a fourteen-year-old transfer student in her second year of middle school who has a deep love for fairy tales and folklore. Her last name, Hoshizora, means "starry sky," which connects to her light-based powers, while her first name, Miyuki, means "happiness," reflecting her core trait. Miyuki is characterized by her cheerful and optimistic nature. She strives to see the bright side of every situation and constantly searches for happiness in her daily life, inspired by the happy endings she reads about in stories. However, she is also notably clumsy, often tripping or bumping into things, and is frequently late to school due to her distractible and daydreaming tendencies. Despite this, she possesses a strong sense of empathy and kindness, and she is very expressive and open about her feelings. This openness is a stark contrast to how she was before the series began, as she used to be more reserved and isolated.

Miyuki's journey begins when she encounters Candy, a fairy from the magical realm of Märchenland, also called Jubiland. Candy is on a mission to find legendary warriors to fight against the forces of the Bad End Kingdom, or Shadow Realm, which seeks to spread unhappiness and revive the evil emperor Pierrot, known as Emperor Nogo. When Miyuki protects Candy from danger, her potential awakens, and she receives a Smile Pact, also called a Glitter Pact, which allows her to transform into the legendary warrior Cure Happy, or Glitter Lucky. As the first member of the team, she naturally becomes its leader. Her transformation is accompanied by the catchphrase "Ultra Happy!" and, in the Glitter Force adaptation, "Another happy ending!"

As Cure Happy, Miyuki's appearance changes: her dark magenta hair becomes a lighter shade and grows into long pigtails, and she wears a pink and white costume with a tiara. Her powers are based on holy light and sparkles. She has extraordinary jumping abilities and can manipulate light energy to attack. Her signature finishing move is the Happy Shower, renamed Sparkle Storm in Glitter Force. Over the course of the story, she gains access to upgraded forms such as Princess Form and Ultra Form, which grant her even greater power.

Throughout the series, Miyuki's role is to unite and lead her four teammates: Akane Hino (Kelsey), Yayoi Kise (Lily), Nao Midorikawa (April), and Reika Aoki (Chloe). Each girl represents a different element and personality, but Miyuki's boundless optimism and determination act as the glue that holds the team together. She forms a particularly close bond with Candy, who serves as her guide and friend. Her relationships with her teammates are built on mutual support and understanding, and she often inspires them to overcome their own insecurities through her unwavering positivity.

Miyuki's character development is significant. Initially, she is portrayed as a somewhat awkward and overly dreamy girl, but as she faces the challenges of being a guardian of happiness, she grows into a bold and courageous leader. She learns to channel her sensitivity into strength and becomes more confident in her abilities. Her love for fairy tales remains a constant source of motivation, as she believes that even in real life, a happy ending is always possible if one keeps smiling and fighting for it. Her notable abilities extend beyond combat; her greatest power is her ability to bring out the best in others and to spread genuine joy, which is the very essence of the happy ending she seeks to protect.