I got these last night. I was killing the WHM mobs in the area for the new scroll drops, and decided to stick around and try to pop Fyuu. He took a long time to pop - maybe 8-10 rounds of placeholders, and no drop. I logged out for 2 hours and came back, and the second time around he popped after 3 or 4 rounds of placeholders, and dropped the pants.
Will be useful for my lvl42 WHM, although as far as looks go they are truly ugly.