Noriko Nijou enters Lillian Girls' Academy, a strictly Catholic school, under unexpected circumstances, resulting in significant cultural shock. Her deep fascination with Buddhist statues and art sharply contrasts with the school environment, making the uniform and refined student mannerisms initially challenging. A calm exterior masks her straightforward and occasionally fierce temper.

Her plain, jet-black hair gives her the appearance of a traditional Japanese doll, visually opposing Shimako Tōdō's "Western doll" features. Noriko's detachment manifests privately; she calls Shimako "Shimako-san" instead of the customary respectful "-sama" and often uses informal Japanese, defying expected politeness.

In her second year, Noriko becomes Shimako's petite sœur. Their relationship evolves from initial awkwardness to deep mutual care, with Noriko playing a pivotal role in Shimako's emotional growth. During the Maria Ceremony, Noriko secretly holds Shimako's family juzu, intending a private return. This act leads to a confrontation where the Yamayuri Council orchestrates an intervention, culminating in Noriko formally returning the beads and solidifying her bond with Shimako.

A key moment occurs when Noriko pauses to observe Shimako and Yoshino carrying medallions through a window; her gentle expression reveals genuine affection, resolving doubts about her suitability as Shimako's partner and underscoring her integration. Her development shifts from cultural alienation to finding belonging, notably helping Shimako see the school as a "nest" instead of a "cage." Noriko maintains close friendships, especially with Tōko Matsudaira, and cares deeply for both Tōko and Shimako.

Noriko's narrative significance lies in catalyzing Shimako's openness and bridging cultural divides within Lillian's traditions. Her journey illustrates adaptation without compromising individuality, emphasizing quiet resilience over overt conformity.