Yotsuba Nakano is one of five identical sisters. A childhood meeting in Kyoto with Fuutarou Uesugi forged a promise between them to study hard and secure prosperous futures for their families. While this encounter ignited Fuutarou's academic drive, Yotsuba struggled with persistent inadequacy as her own intense studying failed to match her sisters' progress. After her mother Rena's death, these insecurities deepened, leading her to abandon academics and pursue athletic excellence and helping others as alternative ways to stand out and feel valued. She consistently places others' needs before her own, evidenced by overextending herself to assist multiple clubs during school festival preparations, resulting in physical collapse from exhaustion. This compulsion to help stems partly from a deep-seated belief she must earn her place through service, fearing she otherwise holds her sisters back. Despite harboring long-standing romantic feelings for Fuutarou, rooted in their shared past promise, she suppresses them due to guilt and a perception of unworthiness compared to her sisters, whom she believes deserve happiness more. When Fuutarou confesses his love during the festival, she initially rejects him. She flees, convinced that choosing her would betray her sisters and fracture their bond, triggering memories of their Kyoto promise and her subsequent failures, reinforcing her belief she hasn't earned happiness. Fuutarou pursues her, confronting these insecurities directly. He reaffirms her impact on his life and rejects her self-deprecation. This persistence and unwavering acceptance eventually allow her to voice her own feelings. However, she postpones formally beginning their relationship until reconciling with her sisters and securing their understanding and blessing. Following reconciliation, their relationship progresses. Fuutarou proposes marriage at the park swing significant to their past, symbolizing a full-circle moment from their childhood promise. Five years later, preparations for their wedding include her sisters piercing her ears so she can wear their late mother's earrings. During the ceremony, she participates in the quintuplets' final game where Fuutarou successfully identifies each sister before placing the ring on her finger, acknowledging their unique individualities and confirming his choice. Post-marriage development shows increased self-assurance. During a honeymoon in Hawaii, she actively helps a young girl alongside her sisters and Fuutarou, contributing her perspective despite initial difficulty expressing herself. Facing another challenge involving meeting Fuutarou's grandparents, she initially considers relying on Miku's composure but ultimately chooses to confront the anxiety directly, mirroring her sisters' independent approaches to their professional challenges. This signifies a shift towards greater self-reliance and confidence, moving beyond her historical pattern of self-sacrifice. Her character arc culminates in balancing her inherent desire to support others with a newfound ability to acknowledge and pursue her own needs and happiness, supported by Fuutarou's steadfast presence.