Yui married her boyfriend, who had a child from a previous marriage. Initially uncertain and anxious about becoming a stepmother, she was moved by his kindness and warm demeanor, resolving to build a future together. Without having experienced pregnancy or childbirth herself, she steeled herself to fulfill the role of a "mother" and began cohabiting with her shy stepson and husband. "Tatsuya-kun. I'm still a rookie mom, but please tell me anything you'd like me to do?" With these words, Yui welcomed the start of a new life as the mother figure to her sadistic stepson.