- Prim, proper and very beautiful (there were a few instances in the novel where the narration describes her skin as very fair, or even pale, and her complexion "like an antique western doll"), Shimako is the most admired of the first-years. She is the petite sœur of Sei at the beginning of the story and later is her successor. Underneath Shimako's quiet, mannerly exterior lies a surprisingly strong resolve, calm personality and thoughtfulness. During Sachiko's initial attempt to perform the sœur ritual on Yumi in front of the entire student council body, Shimako was the only one who considered Yumi's feelings of being forced to be one, and Shimako was brave enough to voice it out. Despite this, she has her uncertainties about herself. She is even unable to decide whether she should run for the next Rosa Gigantea at first, since she is not the type to lead people, and also because she just wants to work, not so much for the council, but for Sei herself. During the Valentine's Day arc (with reference from the novel), we see that though Shimako is outwardly strong, she realises that she is actually very afraid of losing the relationships she has gained so far, hence explaining how she divulged to Yumi that she feels relationships and sense of belonging are only "shackles". Reminiscent of Sei in her third year, Shimako is unsure of how to find a petite sœur in her second year after Sei leaves. She meets Noriko under the cherry blossoms, like how she first met Sei and later asks her to become her petite sœur.
- Shimako was somber in the first two seasons. But she realises, after a phone conversation with Noriko before her trip to Italy, that her school is no longer a cage, but a nest, i.e. a place she can rest. With this newfound emotional gratification and assurance that Noriko will always be with her, Shimako begins to open her heart to others more, and smile more often. It is also stated several times in the novel that Shimako and Noriko looks like a pair of Western and Japanese dolls, and that Shimako has a feverish passion for collecting ginkgo seeds. In contrast to her placid and serious attitude, Shimako's father (who works as a lead monk in their temple) is a lot more light-hearted and hearty, and he was also the one who encouraged Shimako to be open her heart more.
Shimako's father, Norimichi, was born with a weak body into a Buddhist household. He decided at a young age to become a Buddhist priest like his father and entered training to do so after graduating University. However, Norimichi fell in love with Shimako's mother, Yurina, who was training to become a Catholic nun. Norimichi and Yurina both decided to put aside their respective religions and get married. Norimichi did this without informing his family and left home with the intention of never returning. Unfortunately, Yurina died less than a month after little Shimako's birth. Norimichi tried to raise Shimako on his own but after a year he found that his body was wracked with a fatal disease and returned home to beg for his parents to raise Shimako. His parents agreed to this on the condition that Norimichi be enrolled into a hospital. Unfortunately Norimichi died anyway leaving Shimako in the hands of her grandparents and her young uncle, Masafumi. Masafumi had been Norimichi's younger brother. Shortly before his death, Norimichi requested that Masafumi pass on to Shimako his love for the outdoors. It is evident that Masafumi did this as Shimako is known for her love of Cherry Blossoms and Ginko Nuts (Which she harvests and collects). Shimako was officially adopted by her grandfather making him her legal father and Masafumi her older brother.
Ever since Shimako was little she wished to be a Catholic nun. This did not coincide with her family's Buddhist beliefs so Shimako felt that she should not speak about her aspirations. However, upon entering the sixth grade Shimako announced to her father that she wanted to enter a convent when she turned twelve and told him to disown her. Shimako's father found this to be a little sudden so he compromised with her by having her enroll in a Catholic school (Lilian) to get her accustomed to Catholocism. He wanted Shimako to see if this was truly what she wanted to do with her life. Upon entering Lilian, Shimako didn't tell anyone about her family's religious views. Originally, she planned to leave halfway through high school to go join a convent.
Her personality is said to mirror Sei's.
Shimako is a very beautiful young fair-skinned girl with long mid-wavy light brown hair and blue-gray eyes.
Her relationship with Sei Satou, her onee-sama, is not easily understood. The truth, they are very close and care each other.