Kamijou Shiina serves as mother to Kamijou Touma and wife to Kamijou Touya. Her strikingly youthful appearance often suggests she is half her husband's age despite their near-equal years, a detail observed by her son and Misaka Misuzu. She embodies elegance through ankle-length white dresses, cardigans, and white brimmed hats, enhancing her ladylike "Ojou-sama" aura. Her speech features the polite interjection "Ara, ara" (equivalent to "My, my").

Shiina pursues paragliding as a primary hobby, gaining neighborhood recognition for it. She trains her lungs through swimming at a Kanagawa members-only sports center to support this activity. During flights, she routinely sends Touma aerial photographs of their home. She sleeps deeply, remaining undisturbed by significant noise.

Despite a calm exterior, Shiina displays jealousy when women approach Touya. She indirectly threatens him during flirtations or glances at others, citing his tendency to attract women and blaming him for Touma inheriting the trait. She reciprocates Touya's affections, once permitting him to buy risqué swimwear. She addresses both husband and son with the respectful "-san" suffix.

She agreed to Touma's Academy City transfer due to his extreme misfortune, though specifics remain unclear. While Touya travels for work, she primarily stays home but ventures out for swimming or paragliding. After relocating from a traditional Japanese-style residence to a modern home, their dwelling filled with Touya's collected souvenirs.

During the Angel Fall arc, a spell altered Shiina's form to resemble Index, leading Touma to initially suspect a family prank. Under this effect, she wore revealing swimwear at the beach, distressing Touma. Her paragliding photos later helped him identify a home intruder. In the anime adaptation, she encountered Tsuchimikado Motoharu (disguised as idol Hitotsui Hajime), fawning over him and delaying Touma at a critical juncture.

For the Daihasei Festival, Shiina and Touya visited Academy City to watch Touma compete. She grew jealous when Misaka Misuzu and Oriana Thomson approached Touya, though this interaction sparked a lasting friendship with Misuzu. When Touma disappeared mid-games, she and Touya expressed trust in his decisions to Komoe Tsukuyomi, prioritizing his actions over the competition. They later waited at the hospital after his battle with Oriana.

In the Homecoming arc, Shiina swam with Misuzu at a fitness club, discussing their husbands' absences. She revealed awareness of Touma's presence in Russia via news reports, mirroring Mikoto Misaka's discovery. After Academy City provided evasive answers about Touma, she considered throwing a Blu-ray player at him upon his return, implying prior similar actions toward Touya.

During Gremlin's Tokyo invasion in the Magic God Othinus arc, Shiina and Misuzu became stranded in a sports club amid public panic. Restricted to disaster message boards, Shiina recorded a voice message reaching Touma during his confrontation with Freyja, prompting him to seek allies for her rescue. Later, in Othinus's distorted world where Touma was vilified as humanity's enemy, Shiina and Touya faced trial as his parents. They publicly disavowed him as "absolute evil," vowing to "correct their mistake," contributing to his despair.

Shiina maintains a friendship with Misaka Misuzu, bonding over shared motherhood and youthful looks. During one swim session, they discussed their husbands' frequent absences, unaware both men were entangled in separate global incidents. Her cousin, Otohime Tatsugami, interacted with her during the Angel Fall arc while body-swapped with Mikoto Misaka.