From Dragon Voice Project:

About a robot, Jack, who appears frequently in Shimizu's SF stories. He's a robot with very human-like psyche and he once believed that he was human and he can even consume food, unlike many of the other robots of those times. However, a cruel incident opened his eyes to the truth and he decided to perform bounty-hunting duties on a strange planet. That's where he meets Ruby, who turns into an innocent-looking youngster and a beautiful and seducing woman at night... She's a Photuris – a human tribe that preys on other humans in order to survive...