Violence Jack: Slumking

Kanto Hell Earthquake has demolished the metropolitan completely. After the earthquake, Slum King is kidnapping girls and sell them as sex slaves. Mari is wandering on the devastated field looking for her lover, Ken. But she is also kidnapped by them. While she is tortured and trained as a sex slave, Ken saves her. Ken has become the member of Slum King. The king offers condition to him; in return for releasing her, he has to kill Violence Jack.

(Source: AniDB)