Girl Mistress (1980)

An older yakuza man falls in love with Seru, a high school girl. When he is put in prison, Seru begins working as a prostitute to earn money for the gangster's parole. During her yakuza lover's incarceration, Seru gains a new, young boyfriend. The yakuza discovers the new boyfriend after he is released from prison. Realizing that she will have a better life with her new boyfriend who is not associated with the yakuza, he sacrifices his love for Seru and gives her up.