Yayoi loves her brother. Yayoi's one and only dream was marrying her older brother but her dream got shattered when her childhood friend told her that siblings can't get married. Since then, Yayoi has followed the advice of her childhood friend and has been in a courtship relationship with her brother and limiting herself only to have sex. As long as Yayoi can be together and continue to have sex with her brother, she can be quite happy.