Ubu hada no aijin (2000)

Saiko, a bisexual college student, was in love with Satomi, her father's mistress who had looked after her since childhood. Around this time, her parents began discussing divorce, and her father agreed to his wife's request, resulting in the divorce being finalized. Saiko was shocked, but secretly rejoiced at the prospect of living with Satomi. However, when Satomi and Koji showed no intention of marrying, Saiko grew increasingly frustrated…