Kaoru Shimizu first meets Gorō Honda (later Shigeno) as his elementary school classmate. After an argument reveals Gorō's deep passion for baseball, she joins the Mifune Dolphins little league team, becoming one of his earliest recruits. Initially unskilled, Gorō's underestimation fuels her determination to prove herself; she trains diligently, acknowledging her limitations while striving to improve. Kaoru values teamwork and cherishes the camaraderie baseball brings, persisting despite ridicule from opponents and teammates over her gender and skill. Her resolve leads her to step in as catcher during the crucial finals against Yokohama Little after Komori Daisuke's injury. By this time, she has developed romantic feelings for Gorō.

Entering junior high, Kaoru switches to softball, eventually captaining the Mifune East Junior High team. She initially resents baseball due to Gorō's influence but overcomes this grudge. Considering following Gorō to Kaido High, she changes plans upon learning Kaido lacks softball. Gorō encourages her to pursue her own passion for softball instead. Consequently, she attends Seishu High School and later advises her younger brother, Taiga, to join Seishu's baseball club specifically because of Gorō's presence there. Kaoru enrolls at Kyowa University after high school. During her freshman year winter break, Gorō confesses his feelings and she accepts, starting their relationship.

She marries Gorō Shigeno, becoming Kaoru Shigeno. They raise two children, with Kaoru embracing the role of housewife, supporting her family while Gorō continues his baseball career. Her baseball involvement transitions into supporting her children's own pursuits in the sport.

In "Major: Yūjō no Winning Shot," Kaoru appears within Gorō's flashbacks to their Mifune Dolphins elementary school days. The film's focus on Gorō's later experiences in Fukuoka limits her role to these recollections.