Shioriko Mifune, second daughter of a prestigious wealthy family, trained in Japanese traditions like flower arranging and dance, reflecting her household's cultural values. She initially opposed the Nijigasaki High School Idol Club, challenging Setsuna Yuki for student council presidency with a pragmatic stance prioritizing academic success over passion pursuits. Her proposal to disband the club stemmed from a personal fear of failure, influenced by her older sister Kaoruko's unsuccessful Love Live attempt, which led Shioriko to conceal her own idol admiration.

After experiencing the club firsthand, she overcame reservations and joined as the 10th school idol and 11th member. Becoming student council president after Setsuna, she utilized her talent for identifying strengths and weaknesses to advise students on club activities. Despite a strict, reserved exterior, she genuinely cares about helping others, volunteering at community centers with children and organizing neighborhood cleanups.

In Nijiyon Animation Season 4, Shioriko blends pragmatism with kindness, scolding Karin Asaka for impractical ideas during club activities. She displays gap moe when her cool demeanor unintentionally charms others, such as making Setsuna blush while holding her hand. Her interactions include a dream sequence with Kanata Konoe in Chapter 15 after falling asleep while working, and bonding moments like comparing unitmate Lanzhu Zhong to a little sister during a "best big sister" contest. She participates in lighthearted traditions, including a cat-inspired imitation of Ayumu Uehara in Chapter 2.

Physically, Shioriko has semi-long dark green hair, vermilion eyes, a small yellow hair ribbon, and stands 1.60 meters tall. She belongs to the R3BIRTH unit with jade green as her image color.