Yukiho Kōsaka, Honoka Kōsaka’s younger sister, actively supports efforts to save Otonokizaka Academy. Initially a third-year junior high student, she later joins Otonokizaka High as a first-year during the anime’s second season, residing above her family’s traditional Japanese sweets shop with her parents and sister.

Though often scolding Honoka’s impulsiveness, Yukiho’s deep care shines when she abandons her umbrella to aid her sister after a collapse. Her bond with Alisa Ayase, Eli’s younger sister, leads them to establish a new school idol group following μ's disbandment, driven by mutual determination to forge their own legacy.

Initially hesitant to enroll at Otonokizaka due to its closure threat, Yukiho admires UTX High for hosting the elite A-RISE. However, witnessing Honoka’s relentless passion through μ's inspires her to secretly obtain Otonokizaka’s enrollment guidebook, cementing her choice to attend.

Balancing maturity with endearing awkwardness, Yukiho often embarrasses herself through solitary antics—fumbling with outfit adjustments or rehearsing gestures—unaware of onlookers. Her composed exterior cracks during emotional moments, such as tearfully confronting Honoka about neglecting her health.

The manga reimagines her with shoulder-length hair and idol ambitions, contrasting the anime’s portrayal of her initial indifference to idol culture. Her anime arc concludes with Alisa, resolved to uphold Otonokizaka’s spirit independently, marking their transition from bystanders to proactive guardians of its future.