Mao Hiiragi, a second-year student from Kozu-shima, co-founded the school idol unit Sunny Passion with Yuna Hijirisawa. Their goal was revitalizing their island community, facing population decline, by boosting its popularity through idol activities. Sunny Passion achieved early success, winning the Love Live Tokyo regionals and reaching the national finals before Liella!'s formation, indirectly inspiring Keke Tang to pursue school idols in Japan. Their signature song is "HOT PASSION!!" and their official color is passion orange.

Physically, Mao possesses long purple hair with pink highlights, side-swept bangs, purple eyes, and prominent thick eyebrows. Her personality contrasts with Yuna's; she exhibits a calmer, more observant demeanor and tends to be less talkative. Despite Sunny Passion's rivalry with Liella!, Mao consistently demonstrates kindness and support towards them, maintaining a friendly disposition.

Key developments include Mao inviting Kanon Shibuya, Keke Tang, and Sumire Heanna to Kozu-shima for a summer concert. During this visit, she and Yuna privately advised Chisato Arashi that Liella!'s over-reliance on her leadership hindered their individual growth, noting their dancing lacked enthusiasm and personal expression. Mao later shared insights about Sunny Passion's community-oriented approach, explaining how local students helped build their stage due to the island's limited population, which inspired Kanon during lyric writing.

Mao engaged in meaningful conversations with Kanon about motivations for being a school idol, emphasizing that passion alone is a valid reason beyond institutional support. She also expressed curiosity about Chisato's decision to remain separate from Liella! after learning about her dance background. Competitively, Mao and Yuna confidently declared their goal of achieving back-to-back Love Live victories to permanently cement Kozu-shima's presence in the event's history. Following Sunny Passion's unexpected loss to Wien Margarete in the Tokyo regionals, Mao acknowledged their opponent's overwhelming talent while reflecting on their own possible complacency.

Later activities saw Mao sharing Sunny Passion's fan-naming origin story when Liella! sought naming advice, showcasing their grassroots growth through consistent video outreach. Ahead of national tournaments, she expressed gratitude toward Kozu-shima while previewing community-built stages, reinforcing her ongoing commitment to promoting the island. Mao continued supporting Liella! as they progressed in competitions, observing their performances during critical finals.