Short answers, pulled from the story.
The main characters are Retro and Pandy, two amnesiac strangers who awaken naked on a Tokyo street with lethal martial arts skills. Retro has a television screen for a head, while Pandy bears a panda-like mutation.
The film begins on a ruined Earth street and moves to Dead Leaves prison on the moon. The prison serves as a grotesque factory for genetic experimentation and human cloning under the rule of Warden Galactica.
Dead Leaves prison functions as a facility for genetic experimentation and human cloning rather than simple incarceration. The warden Galactica treats inmates as expendable resources to be recycled into new life forms.
Guards 666 and 777 are super-powered enforcers whose bodies are walking arsenals designed to crush any hope of escape. They are eventually absorbed by Galactica to transform her into a giant caterpillar.
The mutant child rapidly ages from a baby to an old man and enters the giant caterpillar to destroy it from within. He sacrifices himself to ensure the safety of Retro and Pandy before the station explodes.