Noriko Ikawa is the 19-year-old younger sister of Tsuyoshi and Keiko Ikawa, attending Ishigami University as a college student. Despite her youth, she demonstrates maturity and responsibility through consistent household contributions to support her busy family. Her relationship with Tsuyoshi is particularly close; she offers steadfast emotional support, listens to his concerns, and motivates him during difficulties. Though occasionally rude or caustic toward him, she acknowledges his boundaries and strives to improve as a sister, such as learning cooking under his tutelage to share domestic duties.

Academically exceptional, Noriko ranks among her class's top students while also excelling as a tennis player. These dual commitments create tension when she must choose between a pivotal tournament and a crucial university lecture, ultimately prioritizing her education. Her perceptiveness captures overlooked details, blending intelligence with empathy to comfort Tsuyoshi in emotional distress. Personality assessments suggest Enneagram Type 1w2 traits, indicating her perfectionism, rule adherence, and urge to correct errors, though this inflexibility sometimes strains relationships. Conflicting MBTI analyses propose either ENTP or ISFJ, the latter underscoring her loyalty, quiet diligence, and avoidance of confrontation.

In family dynamics, Noriko and Keiko receive maternal favoritism from Yoshiko, gaining more attention and praise than Tsuyoshi. Noriko contrasts with Keiko as the "tomboy" to her sister’s "girly girl" persona. A time-travel incident reveals Tsuyoshi and Tsukasa encountering their younger selves twelve years prior, uncovering Noriko’s childhood bond with Tsukasa and her early romantic interest in him. Her romantic inclinations favor non-Japanese foreign men.