User blog comment:Gundam Legilis/Volume 1 Weapons In Depth- Penny's Swords/@comment-50.175.158.72-20140723013235/@comment-3146930-20140723094624

Maybe the strings are the way that Penny sends commands to the swords. Then because they are almost invisible, it makes it harder for people to see them and they instead focus on the swords themselves or Penny. They may also be made from some kind of super strong material as they could be used as ropes to pull down a small plane.