Sex Hunter: Wet Target (1972)

While rotting away in jail, Okamoto learns of the death of his beloved sister, Natsuko. Violently assaulted by a group of U.S. military men during a drunken joyride, she was found dead by local authorities. Haunted by the tragedy, Okamoto escapes from jail to hunt down and kill those who destroyed the life of his sister. What he uncovers during his investigation is much more horrifying than he could ever imagine...