Sawako Sekijou is a high school student at Ichinose Academy and president of the Science Club. She sports long brown hair, usually in a bun or ponytail, with reddish-brown or purplish eyes. A distinctive white laboratory coat is her near-constant attire, worn at home, outdoors, and with friends, rarely removed. She maintains a shapely figure and stands slightly shorter than Nariyuki Yuiga.

In middle school, bullying over her academic prowess led Sawako to isolate herself, skip classes, and retreat to the nurse's office. Her outlook changed after observing Rizu Ogata's focused demeanor during a mock exam, inspiring her to disregard others' opinions. She adopted the lab coat as a symbol of her new identity, influenced by a woman who tutored her. She enrolled at Ichinose Academy specifically to be classmates with Rizu and aimed to attend the same science-focused university.

Academically, Sawako ranks second in her class, excelling in chemistry and science, just below Rizu. She invented a super glue lasting over 15 hours. Beyond academics, she demonstrates high observational skills, recognizing subtle changes in others. She also possesses literary knowledge, identifying references like "Rashomon." Her understanding of interpersonal relationships allows her to deduce Rizu's affection for Nariyuki and employ seduction tactics when necessary.

Sawako exhibits a calm, logical, and often blunt demeanor. She rarely experiences embarrassment, even in revealing situations like wearing only a towel near Nariyuki or showering openly. She addresses others formally, using full names. Privately, sensitivity surfaces, such as crying during romantic movies. She harbors deep admiration for Rizu Ogata, initially viewing her as a rival but striving to become her closest friend. For over two years, she struggled to approach Rizu until a mistaken email from Fumino Furuhashi facilitated their connection. After declaring herself Rizu's "best friend," she filled her room with Rizu memorabilia and prioritized Rizu's happiness, supporting Rizu's romantic feelings for Nariyuki despite her own implied attachment to Rizu.

Sawako's family background involves her parents' strained relationship, which she mistakenly attributed to her loneliness. Her mother, Keiko, is gentle but indecisive; her father remains largely undescribed. After learning her mother planned to leave, Sawako concealed her sadness until Nariyuki encouraged her to reconcile. This resolution allowed her to become more open, eventually using first names for Rizu and Nariyuki.

Following high school, Sawako passed the entrance exam for Yuzuruha University and became roommates with Rizu. Their friendship deepened, evidenced by addressing each other by first names. Additional details include her birthday on August 3, childhood inspiration from a chemistry set, skill at crane games in arcades, and low alcohol tolerance leading to easy intoxication. Her name incorporates wordplay related to mathematical terms like "product" and "sum."