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. 

At Lillian Girls’ Academy, a renowned all-girls Catholic school, pairs of girls become soeurs, or “sisters”, in order to support and guide each other during their time at school. The shy Yumi Fukuzawa thought she was far too ordinary to attract a soeur as popular and beautiful as Sachiko Ogasawara, but for some reason, Sachiko has set her sights on Yumi — but why does she want to become Yumi’s soeur, anyway, and just what will become Sachiko’s soeur entail? 
 
(Source: Maiden Japan)

The second season of Maria-sama ga Miteru. 
 
The spring term is beginning for the students at Lillian Girls' Academy. Friends are reunited, but for the Yamayuri Council, it's a bittersweet time. Yoko, Eriko, and Sei are busy preparing to depart Lillian while Sachiko, Rei, and Shimako are doing their best to ensure that their dear sisters receive a memorable commencement. 
Sei's departure will leave a sizable hole in the White Roses, and filling it won't be easy. But is there anyone who could appeal to Shimako enough to become the next Rosa Gigantea en bouton? 
(Source: RightStuf)

The fourth season of Maria-sama ga Miteru. 
 
Life for the young women at Lillian Girls’ Academy couldn’t be more exciting! The Yamayuri Council is working on a theater production with the all-boys Hanadera Academy, and the school festival is quickly approaching. But Yumi’s duties pale in comparison to the task assigned to her by Sachiko: choosing someone as a petite soeur! Will she be able to handle the pressure of such a monumental decision, or will Yumi crumble under the weight of the Council’s — and Sachiko’s — expectations? 
 
(Source: Maiden Japan)

The third season of Maria-sama ga Miteru. 
 
Summer has arrived at last, and with it comes the promise of summer break for the students of Lillian Girls’ Academy. Sachiko and Yumi retreat to the summer home of the Ogasawara family for a season of rest and relaxation, but their rosy trip soon sours when some old friends of Sachiko’s unexpectedly drop in. These wealthy snobs turn up their noses at Yumi and Sachiko’s relationship — and if Yumi isn’t careful, her blissful summer at Sachiko’s side could come to an abrupt and tearful end. 
 
(Source: Maiden Japan)

A series of specials included on the Maria-sama ga Miteru DVD releases.

Maria-sama ga Miteru's story revolves around the students of the Lillian Catholic school for girls, and can be considered character-driven, focusing on interactions between the characters rather than any sort of ongoing plot or goal to attain. At Lillian Girls' School, there is a tradition known as the sœur system (sœur being French for "sister" ) , in which a second, or third-year student, the grande sœur ("big sister" ) , will give her rosary to a junior student, the petite sœur ("little sister" ) , and promise to look after them and guide them.
 
When the story begins, Yumi Fukuzawa, a new first-year student admitted to Lillian, is praying in front of the Virgin Mary statue near the school entrance when she is suddenly approached by a cold second-year student named Sachiko Ogasawara who straightens Yumi's uniform ribbon. This seemingly simple act of kindness stays with Yumi the rest of the day, and she speaks of her meeting with Sachiko to her friends during class and lunch. After school is over, Yumi's classmate Tsutako Takeshima meets with Yumi to show her that she took a photograph of Yumi's meeting with Sachiko earlier that morning. Yumi asks if she can have the photo, but Tsutako says she will give her the snapshot under two conditions: one being that Tsutako can display it at the upcoming school festival, and two being that Yumi get Sachiko's permission to do so as well. Yumi agrees to this, which sets in motion a series of events involving the entire Yamayurikai — the student council of the school. A few weeks after first meeting Sachiko, Yumi accepts Sachiko's rosary and therefore agrees to become her petite sœur.
 
This officially inducts Yumi into the Yamayurikai where she assists them in school matters at the same level as the other two petite sœurs — Yoshino Shimazu, and Shimako Toudou — who are the petite sœurs of Rei Hasekura, and Sei Satou respectively. Through her activities in the Yamayurikai, Yumi becomes closer to the other members and generally finds her experiences with the group to be enjoyable.

Specials of Maria-sama ga Miteru: Haru released on the DVDs only.

The setting is Lillian Academy, a private Catholic all-girls school where the student council is known as the Yamayurikai (Mountain Lily Council) and younger students are taken under the wing of older students through a system known as the "soeur system" ("soeur" is French for "sister"). The main character, Yumi, who is basically a nobody, suddenly finds herself interacting with the members of the Yamayurikai and their soeurs, most notably her crush, the talented, beautiful, and withdrawn Sachiko...


Youko Mizuno