Itsuki Myōdōin, known as Cure Sunshine, stars in *Heartcatch Pretty Cure!* and appears in the film *Eiga Tropical-Rouge! Precure: Yuki no Princess to Kiseki no Yubiwa!*. A second-year student and student council president at Myōdō Academy, she initially presents as male to uphold her family’s dojo legacy after her brother Satsuki’s illness prevents him from inheriting the role. Despite her natural affinity for dolls and fashion, Itsuki adopts masculine attire and mannerisms, suppressing her identity. Her internal struggle surfaces when she hides a gifted plush bunny to protect her princely image. This conflict withers her Heart Flower, allowing antagonist Cobraja to create a Desertrian from a bronze statue. During the incident, her true gender is revealed. After Cure Blossom purifies her Heart Flower, Itsuki joins the fashion club to explore her femininity.

Encouraged by Tsubomi and Erika, she designs a dress. Though initially dismissing it as frivolous, Satsuki affirms it suits her. Itsuki’s perspective shifts when she defends a boy named Hiroto, realizing martial arts can protect others. She joins the fashion club, symbolizing her integration of strength and femininity. To rescue her friends and save Satsuki—whose Heart Flower was stolen—Itsuki becomes Cure Sunshine. Fairy partner Potpourri identifies her as the third Cure. Hesitant at first, she embraces the role upon seeing Satsuki transformed into a Desertrian. Drawing inspiration from sunlight, a symbol of her brother’s encouragement, she adopts the name "Cure Sunshine." Her solar-based powers feature the catchphrase "I will heal the darkness in your heart with my light!" Her Heart Flower is the peony, representing rebirth, while her theme flower is the sunflower.

Wielding the Shiny Perfume for transformations and attacks like Gold Forte Burst, Cure Sunshine faces her past self during the Super Silhouette trial. This version accuses her of abandoning martial arts. Itsuki resolves the conflict by declaring she honors her brother while embracing her true self, unlocking her upgraded form with rainbow wings. Later, she declines re-election as student council president to prioritize Cure duties. In the final battle against Dune, she reunites with Satsuki after the world’s desertification, strengthening her resolve to protect loved ones. In *Eiga Tropical-Rouge! Precure: Yuki no Princess to Kiseki no Yubiwa!*, Cure Sunshine and the Heartcatch team aid the Tropical-Rouge Cures in Shantia, a snow kingdom, collaborating to defeat a monster imprisoning inhabitants.