TV Special
Description
Youko Mizuno served as Rosa Chinensis on the Yamayurikai student council at Lillian Girls' Academy. Attending since middle school, she gained early attention delivering the welcome speech as an outside enrollee. Calm, reserved, sharp, and observant, she often wore a subtle smirk and possessed a mischievous streak. Her leadership maintained stability within the sometimes volatile council.

Tricked during her second year of high school by the previous Rosa Gigantea and Rosa Chinensis, Youko took an interest in the internally conflicted Sachiko Ogasawara. Recognizing Sachiko's struggles, Youko took her on as petite sœur. She intervened in Sachiko's life, prompting her to quit stressful after-school lessons and frequently admonishing her for suppressing emotions and opinions. This mentorship later inspired how Sachiko guided her own petite sœur, Yumi Fukuzawa.

Youko shared a close, complex bond with Rosa Gigantea, Sei Satou, whom she met in middle school. Despite Sei's initial dismissal of her as a meddler, Youko persistently reached out, especially during Sei's difficult relationship with Shiori. She facilitated their communication, ensuring Shiori left Sei a letter upon departure. Though never openly acknowledged, Youko harbored implied unrequited feelings for Sei, a popular dynamic among fans. She encouraged Sei to take Shimako Toudou as petite sœur, believing it beneficial for both the council and Sei.

Her meddlesome tendencies stemmed from a genuine desire to help. She orchestrated a bet involving a Cinderella play during a school festival to help Sachiko overcome her aversion to men and create an opportunity for her to find a successor. This plan succeeded, leading to Yumi becoming Sachiko's petite sœur. Before graduation, Youko expressed a wish to see the Roses Mansion filled with ordinary students, fulfilled during a Card Hunting Game event.

Prior to graduating, Youko asked Yumi to look after the stubborn and "uncute" Sachiko. She later expressed subtle jealousy over Sachiko and Yumi's deep bond but affirmed she would always consider herself Sachiko's onee-sama. During Sachiko's grandmother's funeral, Youko's mother tasked her with meeting Yumi to explain the situation and accompany her to the family residence.

After graduation, Youko pursued law at university, tearfully admitting she would have preferred liberal arts but chose law to better enable her to help people, reflecting her chronic hero syndrome. Her name, meaning "lotus flower child," and surname Mizuno, meaning "water field," carry symbolic weight in her characterization.