Sawako Sekijou attends Ichinose Academy as the Science Club president. She has long brown hair, usually in a bun or ponytail, reddish-brown eyes in the anime, and is slightly shorter than Nariyuki Yuiga with a shapely figure. Her defining trait is her near-constant wear of a white laboratory coat, rarely seen without it even at home or outdoors.

Significant bullying and isolation during middle school, stemming from her high academic performance, caused her deep hurt. She began skipping classes, seeking refuge in the nurse's office out of loneliness. A pivotal moment came while observing Rizu Ogata's focused confidence during a mock test, inspiring Sawako to embrace her own path without regard for others' opinions. This motivated her to adopt the lab coat as a symbol of confidence and enroll at Ichinose Academy specifically to be near Rizu.

Sawako presents a calm and collected demeanor, rarely showing embarrassment even in compromising situations like being seen half-naked. She addresses others formally by their full names and possesses keen observational skills, detecting subtle emotional shifts or deducing romantic feelings. Despite her composure, she harbors deep sensitivity, often crying during emotional moments like romantic movies. Academically, she ranks second in her class, excelling in science and chemistry where she invented a long-lasting super glue. She also possesses unexpected literary knowledge, recognizing references like "Rashomon."

Her relationships are heavily defined by intense admiration for Rizu Ogata, viewing her as both a rival and inspiration since middle school. Sawako engages in stalking and covertly photographing Rizu, self-identifying as Rizu's "best friend." She prioritizes Rizu's happiness above her own, even cutting short outings to facilitate time between Rizu and Nariyuki. While she occasionally flirts with Nariyuki to test his interactions with Rizu, she lacks romantic interest, maintaining a comfortable platonic dynamic. She respects his tutoring abilities, labeling him "too generous." Her acquaintanceship with Fumino Furuhashi and Uruka Takemoto (who nicknames her "Sawa-chin") is amicable but less central.

Character development occurs through a family subplot where she initially masked distress when her mother considered leaving home, feigning indifference while feeling profound loneliness. Encouraged by Nariyuki and Rizu, she reconciled with her parents, leading to greater emotional openness. Post-high school, she passed the entrance exam for Yuzuruha University and became roommates with Rizu, transitioning to using first names as a sign of deepened friendship. In Rizu's narrative conclusion, Sawako assists in resolving Rizu's familial conflicts, remaining a close presence and eventually cohabiting with Rizu and Nariyuki after they start a family. Her journey involves overcoming isolation, valuing genuine connections, and supporting others selflessly.