In the beginning of the series, Yoshino is a girl who was very ill and cared for constantly by her grande soeur, Rei. Yoshino, however, is very independent and in some ways tomboyish, despite her sickly status and feminine appearance. After her heart surgery, she becomes more energetic through out the series. In addition to being Rei's petite soeur, Yoshino is also her cousin and next-door neighbor. Theirs is a somewhat rocky relationship, since Yoshino is eager to spread her wings, whereas Rei would like to protect her from the world's hardships. In the first season, Yoshino is Rosa Foetida en bouton petite soeur, her grande soeur being Hasekura Rei. In the second season, Yoshino becomes Rosa Foetida en bouton. She has no petite soeur yet. (Source: Wikipedia)
Prim, proper and very beautiful, Shimako is the most admired of the first-years. She is the petite soeur of Sat� Sei at the beginning of the story and later her successor. Underneath Shimako's quiet, mannerly exterior lies a surprisingly strong resolve. However, Shimako is perhaps the most gentle of the three girls of her year in the Yamayurikai. In the first season, Shimako is Rosa Gigantea en bouton, her grande soeur being Satou Sei. In the second season, Shimako becomes Rosa Gigantea, her petite soeur being Nijou Noriko. (Source: Wikipedia)
A distant relative and fan of Sachiko. She arrives at Lillian during Yumi's second year. Touko is a member of the Drama club, and nicknamed Mechanical Drill by Satou Sei for her corkscrew pigtails. In the beginning of her first year Touko causes some strain in the relationship between Yumi and Sachiko. However, it is apparent later on in the year that she may become Yumi's petite soeur. (Source: Wikipedia) Touko later wins the second card hunt when she half-accidentally makes Yumi uncover her card, thus winning the date with Yumi. She does so by basically asking Yumi to make her a petite soeur, and the recurring date practically ensures that Touko will become just that. In the same episode, we learn that Touko is also not the real daughter of the Matsudaira family, which made her the target for a lot of harsh words from the other close families. Despite this, her adopted family loves her like she was their own biological daughter, who adopted her after her parents died in a car crash, leaving her as the sole survivor. It's also revealed that Touko wants to take over the family hospital after her grandfather, but she wasn't allowed to do so yet, due to her young age. She will most likely be given that opportunity at a later date, though.
A young girl with a fascination with Buddhist statues and art. She enters Lillian Academy (a strictly Catholic institution) by mistake. She has a fierce temper that contradicts her calm exterior and becomes Shimako's petite soeur as Shimako enters her second year. (Source: Wikipedia) In the second season, Noriko becomes Rosa Gigantea en bouton, her grande soeur being Toudou Shimako.
Rei's grande soeur; one of the most well-respected of the Yamayurikai. She is very gifted and good at almost everything, although she is also enigmatic and eccentric. She has a large forehead, which Sei made fun of when they were young, which began their rivalry. She said once that she chose Rei as her sœur to see if anything interesting would happen. She often has friction with Yoshino, as the younger girl is jealous of her bond with Rei. Eriko has four older brothers. After leaving Lillian, she studies Arts. She hates the dentist above all else. (Source: Wikipedia)
Tamaki's younger, perverted brother.
Haruka's younger sister, She initially sees both Takayuki and Mitsuki as older siblings until she finds out they have been seeing each other behind Haruka's back. While Haruka is in the hospital, she visits every day since there is no one else that can keep her company, even if Haruka is in a coma. This shows just how much she loves her older sister. She, like Mitsuki, is a powerful swimmer in her own right, but feels as if she can never match Mitsuki. Her intense hatred towards Mitsuki after the accident can be attributed to the feeling of personal betrayal by someone she considered an idol for throwing away her (Mitsuki's) talent and dreams as well as Mitsuki's betrayal of her sister by her sexual relationship with Takayuki. She learns to move on in life and becomes a top swimmer in Japan. (Source: Wikipedia)