Youko Mizuno

Youko entered Lillian during her first year of middle school. Despite coming from an outside schooling system she was asked to give the welcome speech for first year students. She is characterized as being calm but sharp with a mischievous side, in the manga she is described to be "lily" like. Her greatest day was seeing the Rose Mansion filled with ordinary students during the Bouton's card hunt. During Youko's second year of high school, Rosa Gigantea and Rosa Chinensis (Sei and Youko's onee-sama's respectively) tricked Youko into taking an interest in Ogasawara Sachiko. Sachiko, Youko noted, always walked looked like she was fighting internally with something.

With an endless desire to help (or meddle, as Sei put it) people Youko took Sachiko as her petite soeur. She had Sachiko quit her after school lessons (or in the novel, hinted about it) and once scolded her for not expressing her emotions and opinions. Much like Sachiko did to Yumi. Prior to graduating, Youko took Yumi aside and asked her to look after her stubborn and "uncute" little sister. Then later during Sachiko and Yumi's separation she felt slightly jealous of the close bond between them. Youko considers herself to be Sachiko's onee-sama even beyond graduating from Lillian. Aside from her petite soeur Youko is probably closest to Satou Sei.

They met during middle school when Youko approached Sei about joining clubs. Sei asked if Youko too felt alienated from the class but Youko said she simply became interested in Sei. Disinterested in this, Sei called her a meddler. During Sei's relationship with Shiori it was Youko who constantly tried to reach out to Sei. It was also Youko who asked Shiori to leave Sei a letter when she left. Fans have speculated that Youko has an unrequited love for her friend and the Sei/Youko pairing is very popular within the fandom. After graduating from Lillian, Youko attends law school. She tearfully admitted that she would have liked to attend a liberal arts college but it wouldn't have enabled her to help people.