LogFAQs > #880249380

Naked Cartwheels (Start of Battle) - Once every seven weeks, Raiden can show up to battle mysteriously fully human, completely naked. He'll run and cartwheel around the terrain, desperately hoping to avoid being seen. If he makes it to the other end of the terrain, Snake will be there to give him his gear back -- in this case his exoskeleton and weaponry. For some strange reason, all the enemies after Raiden gets his equipment back will be using swords almost exclusively. All enemy mercenaries will have their weaponry replaced with blades for Honorable Samurai Combat.

Note the bolded.