Shimako Toudou enters Lillian Girls' Academy as a first-year student admired for her serene demeanor and striking beauty, characterized by fair skin, long light brown hair, and gray-blue eyes. Her background involves significant familial complexity: born to a Buddhist monk father, Norimichi Toudou, and a mother, Yurina Toudou, training to become a Catholic nun, both abandoned their religious paths to marry. Her mother died less than a month after Shimako's birth, and her father succumbed to illness a year later. Raised by her grandparents and uncle Masafumi, and officially adopted by her grandfather, she grew up in a Buddhist temple environment. However, she developed an early aspiration to become a Catholic nun, leading her to enroll at Lillian. She guarded this dual religious heritage as a secret, fearing judgment from her peers. Initially introverted and somber, Shimako viewed relationships as potential "shackles" due to a fear of abandonment stemming from her parents' deaths. Her reserved exterior masked a thoughtful and resolute nature, evident when she alone advocated for Yumi Fukuzawa's feelings during Sachiko Ogasawara's impulsive sœur declaration. She became the petite sœur of the outgoing Rosa Gigantea, Sei Satō, after initial hesitation. Their unconventional bond, due to contrasting personalities, helped Shimako gradually engage with the Yamayuri Council. Sei provided emotional support without pressure, notably encouraging Shimako to independently decide whether to run for Rosa Gigantea en bouton despite Shimako's self-doubt about leadership. Following Sei's graduation, Shimako experienced profound isolation, perceiving the school as a "cage." Her emotional trajectory shifted when she met first-year student Noriko Nijou under the cherry blossom trees—a location symbolically tied to her first encounter with Sei. Noriko discovered Shimako's religious secret but accepted her unconditionally, becoming pivotal in Shimako's life. This relationship alleviated Shimako's loneliness and catalyzed her emotional openness. Through conversations with Noriko, particularly before a trip to Italy, Shimako redefined the school as a "nest"—a place of safety and belonging. She subsequently smiled more freely and engaged more warmly with others. Shimako formally invited Noriko to become her petite sœur, mirroring how Sei approached her. This act solidified her role as a mentor and her position as Rosa Gigantea. Her development culminated in a quieter confidence, balancing her innate gentleness with the resilience nurtured through her bonds. Her hobbies, such as fervently collecting ginkgo seeds, add nuance, contrasting her dignified appearance with earthy, passionate interests.