S1E63 · The Sisters of the Pitch Dark Planet

The 999 stops at the Pitch Dark Planet, where all light is instantly absorbed. A while after Maetel leaves the train to "attend to private business", Tetsuro is beckoned outside by a figure at his window, who proves to be Miru, a daughter of the planet's ruler. She and her father tell him that Maetel has been kidnapped by Miru's sister Lelan, a deranged but brilliant scientist who plans to use Maetel's brain to launch an artificial sun into orbit, and that Maetel will die unless Tetsuro can infiltrate Lelan's base and kill her. Further, the new sun will doom most of the life on their world, which has never had light in its entire natural history. Tetsuro goes back for his gun, but is taken prisoner by Lelan the instant he steps off the train. His efforts to escape prove futile and Lelan launches the sun. Miru, horribly burned, staggers into the base and tries to shut the sun off but is shot by her sister. Maetel accosts Lelan and accuses her of genocide but she retorts that sacrifices must be made for the greater good. She runs out into the sunlight and is burned to death. As the train leaves, the Conductor reports that 99.99% of the planet's population has perished.