Noriko Nijou enrolls at Lillian Girls' Academy, a strictly Catholic institution, through unforeseen circumstances rather than choice. This abrupt transition immerses her in profound cultural shock as she grapples with the school's antique mannerisms, refined uniforms, and traditions. She retains a deep fascination with Buddhist statues and art, frequently visiting temples for admiration—even journeying to Kyoto for Buddhist art viewing the day before her high school entrance exam. Her appearance presents very plain, jet-black hair styled simply, evoking a traditional Japanese doll. This contrasts distinctly with Shimako Tōdō's "western doll" look. Despite Noriko's calm exterior, she harbors a straightforward and fierce temper. Privately, she avoids polite Japanese with Shimako, addressing her as "Shimako-san" rather than the customary "Shimako-sama" for upperclassmen, underscoring her detachment from Lillian's culture. Noriko first encounters Shimako beneath a cherry blossom tree behind the school auditorium. Her reaction—blushing and pausing—leads Shimako to misinterpret it as awe for the blossoms. Noriko returns regularly during lunch breaks, hoping to see Shimako again. Their relationship blossoms through these meetings, though Noriko's behavior draws scrutiny from others, including Yamayuri Council members. When Rei Hasekura directly questions her—"Do you like Shimako?"—Noriko affirms it. She later becomes Shimako's petite sœur after Shimako enters her second year, formalized by the rosary ceremony in Volume 10. Noriko regards the ceremony as a formality, recognizing Shimako's emotional attachment to the rosary. She pragmatically offers to treat it as a loan, stating it holds no personal significance for her compared to its weight for Shimako. Noriko uncovers Shimako's secret background: residence in a Buddhist temple household. Protecting this secret becomes instinctive. When orchestrated events risk exposure, Noriko deliberately takes full blame to shield Shimako, proving fierce loyalty. This act tests her suitability as Shimako's petite sœur, a trial she passes. Her devotion intensifies as she vows to remain by Shimako's side until graduation. During the Maria Festival, after Shimako reveals her temple upbringing publicly by gifting prayer beads containing a Buddhist statue, Noriko reacts by running to embrace her passionately. She later clarifies her defense of Shimako stems from refusing to part with her. Noriko acknowledges her own conceit in believing Shimako needs her. She advises Shimako to hold Yamayuri Council companions with one hand and Noriko with the other, symbolizing their bond. Noriko becomes Rosa Gigantea en bouton, succeeding Shimako within the student council structure, and anticipates significant council responsibilities. She maintains close friendship with Tōko Matsudaira. Her evolution shifts her from a skeptical outsider to someone deeply integrated through her bond with Shimako. She preserves her directness and calm exterior while directing fierce protectiveness into unwavering support for Shimako.