Noriko Nijou

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.