Arisa Ishino attends high school alongside classmates Hikari Tsutsui and Iroha Igarashi. She sports light-peach hair, usually tied in a ponytail with swept bangs, reaching chest or hip length when loose, and has brown eyes. Seven years post-graduation, she cuts her hair to chin-length. Her school uniform is a blue skirt, white shirt, and red bow.

Initially, Arisa openly scoffs at Hikari's otaku lifestyle. Despite this blunt honesty, she possesses a fundamentally friendly nature, evolving into a confidant who offers relationship advice to both Hikari and Iroha, despite her own history of poor romantic judgment. She recognizes her tendency to trust exploitative men yet struggles to break the pattern.

Her friendship with Hikari began in grade school, bonding over his anime-style drawing skills. During middle school, she distanced herself to protect her social reputation, chasing multiple boyfriends who often took advantage of her.

Reconnecting with Hikari during high school after a chance encounter, Arisa gradually shifts from criticizing his relationship with Iroha to becoming a supportive friend. She develops strong feelings for Mitsuya Takanashi, persistently pursuing him despite repeated rejections. Over time, Mitsuya reciprocates, leading to an on-again, off-again relationship lasting seven years. Following several breakups and reconciliations, Arisa becomes pregnant and insists on marriage. She adopts the surname Takanashi and gives birth to a son. Mitsuya occasionally uses her maiden name "Ishino" as a nickname.

Arisa is significant as Iroha Igarashi's first female friend. Her maiden surname, Ishino, combines the characters for "stone" and "field," while her married surname, Takanashi, means "tall pear."