Early Spring Story aka soushun monogatari (1985)

Seventeen year old high school girl Hitomi (posing as a 20 year old university student) becomes romantically involed with 42 year old executive Shinji Kajikawa. Hitomi discovers that Kajikawa was her mothers ex love interest and that he left her mother to advance his career. At first Hitomi tests Kajikawa's memory of her mother. Eventually she confronts him about her mother and at the same time aggressively seduces him. But is Hitomi seducing Kajikawa for heself or for mother?