Pan-Dora are two large swords, with the only difference being that one is magenta and the other is teal, and are described to have an eerie shape with a guard that has a pattern resembling an eye, with both patterns together resembling a monster's eyes. In the anime, Claudia's eyes appear to take on those colors when she uses it.
Pan-Dora's assumed power is the ability to see up to 300 seconds into the future. However, this 300 seconds is stocked, meaning that if the user uses 10 seconds, they are left with 290 seconds to see the future with. One second can be gained back in about three days, as long as the user is still in contract with Pan-Dora, making strategy vital to its use. Claudia explains Pan-Dora's ability as the ability to go through trial and effect with no immediate consequences. As her actions change, so do her clairvoyance.
The cost of Pan-Dora was thought to be the user seeing a way they can die in their dreams every time they sleep. As of volume 3, Claudia mentions to have died over 1200 times. She also mentions that the dreams seem to melt away as she wakes, leaving behind only a fragmentary memory, the fear and pain of the nightmare, and a sense of malaise.
However, later on Claudia reveals during her meeting with Ladislav that future sight isn't Pan-Dora's actual ability, only a side effect, and its true cost is the future itself.