Kaoru Shigeno, born Kaoru Shimizu, begins her journey as a classmate of Goro Shigeno in elementary school and eventually becomes his wife and the mother of their two children, Daigo and Izumi. Her early life is defined by her initial encounter with baseball, a sport she takes up after seeing Goro's intense passion for the game. She is the first person Goro recruits to the Mifune Dolphins little league team, where she proves her dedication by cutting her hair short to play more easily. During the little league finals, she steps in as the team's catcher, demonstrating her willingness to take on challenging roles for the sake of the team. As she advances to junior high school, she transitions from baseball to softball, becoming the captain of her school's team. A significant part of her motivation during this period is her desire to stay connected to Goro, though she ultimately chooses to follow her own love for softball rather than trailing him to a high school without a team for her. This leads her to attend Seishu High School, the same school Goro would later attend, and she later goes on to Kyowa Women's University. After Goro confesses his love during her freshman year of university, the two begin a relationship that culminates in marriage.

Kaoru possesses a cheerful and warm personality, though she can also be short-tempered at times. She is deeply caring and loyal, especially toward her friends and family, with Goro being a central figure in her life for as long as she can remember. Her actions consistently show a person who is passionate about her own athletic pursuits, earning her a reputation as a softball fanatic to match Goro's status as a baseball fanatic. She is also a supportive presence, whether it is encouraging her younger brother, Taiga, to join Seishu's baseball club or, in her role as a mother, managing the household as a housewife while her husband continues his baseball career. Her role in the story of Major 2nd is that of a supporting family member. She is no longer a player on the field but the steady foundation of the Shigeno household, providing a stable home environment for her children and supporting her husband from the sidelines.

Her most significant relationship is, of course, with Goro Shigeno, the former protagonist of the original Major series. Their connection begins in childhood and evolves from teammates to a romantic couple and finally to marriage and parenthood. As a mother, she is a central figure in the lives of her children, Daigo and Izumi. Kaoru also maintains a friendship with Toshiya Sato, Goro's longtime friend and rival, and has a considerate relationship with teammate Fuji, who looks out for her during her brief return to catching and encourages Goro to acknowledge her feelings. Her development from a young girl who first picks up a baseball glove to a dedicated athlete and, eventually, a supportive wife and mother is a complete arc. Her notable abilities include her skill as a catcher in little league and later as the captain of her junior high softball team. Her strong throwing arm and reliable catching ability allow her to handle Goro's powerful pitches, a testament to her own athletic talent. This background as a catcher also gives her a deep, practical understanding of the game of baseball, a perspective she carries with her into her adult life.