Kyoko Otonashi, born Kyoko Chigusa, is the daughter of middle-class parents Ritsuko and an unnamed father. She developed feelings for her high school geology teacher, Soichiro Otonashi, which became mutual love. Despite parental resistance over their age difference, they married shortly after her high school graduation when she was around eighteen. Soichiro died in an accident only six months into their marriage, leaving Kyoko a widow. This loss led her to vow never to marry again to preserve his memory.

Following her husband's death, she retained his surname and moved into Maison Ikkoku, a boarding house owned by her father-in-law, Mr. Otonashi. She became its manager at age twenty-one, residing in the manager's room, labeled room zero to reflect the "nothing" meaning in her surname. Her dog, originally named Shiro by Soichiro, was renamed Soichiro after his death.

Initially, Kyoko presented herself as sweet, polite, and dedicated to her duties, though she possessed jealous tendencies and a volatile temper when provoked. Her early interactions with resident Yusaku Godai were marked by viewing him as a younger brother. Godai's drunken declaration of love forced her to confront his romantic feelings. This began a struggle to reconcile her attachment to Soichiro with her growing affection for Godai.

Kyoko navigated multiple romantic challenges. She briefly dated her tennis coach, Shun Mitaka, partly due to parental pressure favoring Mitaka. Her feelings for Godai persisted, often surfacing as jealousy during his interactions with women like Kozue Nanao or Ibuki Yagami. Misunderstandings frequently strained their relationship, such as Kyoko misinterpreting Godai's intentions with Kozue or the "love hotel incident" involving Akemi Roppongi. These conflicts sometimes led Kyoko to lash out or temporarily leave Maison Ikkoku.

Over time, Kyoko gradually acknowledged her love for Godai, particularly as he matured into a responsible kindergarten teacher. Her acceptance required emotionally setting aside the idealized memory of Soichiro, culminating in a symbolic farewell where she stated, "Goodbye, Soichiro." She eventually married Godai, changing her surname to Godai, and they had a daughter named Haruka. As a mother and wife, she found serenity and closure regarding her past, affirming Maison Ikkoku as the place her new life began.

Her relationships extended beyond romance. She maintained a familial bond with her supportive father-in-law, Mr. Otonashi. She tolerated the eccentric tenants of Maison Ikkoku—Hanae Ichinose, Akemi Roppongi, and Yotsuya—who often complicated her life with their meddling and parties. Despite their antics, they formed a close-knit community, and their interactions sometimes provided pivotal pushes toward her reconciliation with Godai.

Kyoko's character is defined by her transition from grief-stricken widow to a woman embracing new love.