Prim, proper and very beautiful, Shimako is the most admired of the first-years. She is the petite soeur of Satō 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.