Yoshiko Kouzuki married into the Kouzuki family as the wife of Keiichirou Kouzuki following his first divorce. She serves as stepmother to both Kazuna Kouzuki and Yura Kouzuki, though she raised only Yura. This selective upbringing resulted in minimal interaction and communication between Yoshiko and Kazuna. Her relationship with Kazuna involves child neglect, contributing to the family's strained dynamic.