Natsume attends Yamabuki High School as a second-year art student in Class B, while Sae and Hiro are in Class A, restricting their school contact. She lives with her mother and commutes daily via a 10-minute bicycle ride to the nearest station followed by a 42-minute train journey. Her appearance features teal hair styled in a braid resting on her right shoulder, with matching teal eyes consistent with others.

Natsume demonstrates natural tutoring aptitude, enjoying assisting underclassmen with homework during visits to Hidamari Apartments. Her specific artistic interests and club activities remain unspecified, though she plans to attend Ama Art University—the same institution as Hiro.

Socially, Natsume exhibits a polite and pleasant demeanor when Sae is absent, maintaining friendships with classmates for lunch and study. These friends recognize her feelings for Sae and encourage direct approaches. Her primary dynamic centers on an unrequited crush on Sae, manifesting as a fabricated rivalry in Sae's presence. This tsundere behavior features nervous fluster replacing hostility during intimate interactions. Small kindnesses from Sae, like receiving a leftover sandwich, make her privately euphoric. Notably, Natsume knows Sae’s romance magazine pen name "Aya Tachibana" and authored the first passionate fan letter praising Sae’s work.

Natsume evolves from minor comic relief to nuanced emotional expression. Initial jealousy of Sae and Hiro’s closeness fuels rivalry posturing, though interactions soften as she accepts their dynamic. A pivotal graduation moment sees her drop the tsundere persona, tearfully confessing her desire to remain friends with Sae and embracing her directly—an unprecedented physical contact reflecting significant growth. This scene resolves her arc by affirming genuine affection beneath the rivalry.

Post-graduation, Natsume enrolls at Ama Art University, suggesting ongoing proximity to Hiro.