Brains.When Pidge can't get into contact with his brother Chip on Intergalactic Ninja Appreciation Day, he gets worried about him and travels with the rest of the force to his home planet of Balto where every inhabitant is a ninja-scientist. While there, they discovery that everyone has fallen off the grid going into stealth mode and turned into mindless "ninja-scientist zombies" with an appetite for Voltron Force brains. They find the root of the cause when King Lotor returns and is more powerful than ever when he's able to transform into a samurai robeast which Voltron must defeat with Larmina's martial art form with her blazing katana in order to save the citizens from Maahox's brain vacuum for sucking out information about Voltron.