Yo Kenji ,i make a guide with which you can find them
First try it: Theres a set of panties in the dukes demense in the ladies room.
(if you don't found it...try it:
Heavens peak fort. I found a room with 3 chests...if you don't found it...do like this..
I saved after arriving at the fort for the second time trying to pick up another pair of Panties, to which I only got a Nimble Ring and another Hunter's Bow. Later on, I got killed by a Chimera and was forced to reload back at the fort, so I went in and opened the chest again to find different loot than what I had before, so I simply reloaded and opened it again, noticing that it was in fact, different loot.
So with that said, it seems that if you save the game before you open a chest, you can reload and get different loot if you're displeased with it at first. So far, the loot in the bottom floor chest can be:
And it also turns out that the chest on the top of the castle can be more than just a Hunter's Bow. So far, I've found Red Knee Boots, and a Blue Kilt-something...
you have a Ps3 version Kenji? because if not...i can get the panties for you with a Editor for Xbox360 version..