Amy to Yobanaide (1997)

This is a story about a high-school girl named Emi, who fell in love with her younger step-brother. Finally, on her eighteenth birthday, she decides to tell him about her feelings. But suddenly, debt collectors arrive and confiscate everything your father possessed. Tomomi, Emi's step-brother, disappears. Now Emi must find him, her only true love, and to confess to him her feelings. But on her journey, Emi discovers a different personality inside herself. This other person is called Amy. While the true Emi is a shy, modest girl, her Amy part cares mostly about one thing: to make real her wildest sexual fantasies...