Yuna Hijirisawa is the cheerful and talkative co-founder of the school idol group Sunny Passion, which she established with Mao Hiiragi to revitalize their hometown of Kozushima, an island facing population decline. With kind and friendly demeanor, Yuna has yellow-orange hair often tied in a shoulder-length ponytail and bright green eyes, representing the group's yellow image color. She possesses a habit of saving her favorite things for last.

Sunny Passion serves as friendly rivals to Liella! and previously won the Love Live Tokyo regionals, advancing to the tournament finals—an achievement that inspired Keke Tang to move to Japan and become a school idol. The group debuted with "HOT PASSION!!" and adopted passion orange as their unit color.

Yuna and Mao maintain a supportive relationship with Liella!, offering advice and sharing experiences. During Liella!'s visit to Kozushima, Yuna conversed with Kanon Shibuya about school idol motivations, stating that a specific reason is unnecessary and many pursue it simply for the love of singing. This exchange inspired Kanon's lyrics, reflecting Yuna's dedication to her island.

After losing the Tokyo regionals to Wien Margarete, Yuna and Sunny Passion acknowledged the defeat, recognizing they might have let their guard down. They later attended Liella!'s performance in the Love Live grand finals.

The name Sunny Passion was suggested by a fan. The group holds annual summer concerts on Kozushima and uploads videos to increase recognizability.