Tokyo no Casanova(1983)

Tamiko lives with her two brothers, her mom, and her grandmom. It's your typical family, or so she thought. But one day, she finds out Akira, her older brother, is not her brother at all, but the illegitimate child of famous actress Hanyuu Kaori. To make things even more confusing, Akira's feelings towards her isn't the kind towards a sibling, and with his persistence, she finds herself falling in love with him as well. The plot becomes even more complicated when Yukari, Tamiko's friend from school falls for Akira. Yukari though, has a connection with Akira that shocks everyone, including herself...