Hmm... Koa should carry a a PDW for her style IMO. an MP7 should suffice.
I feel Sakuya fits the bill for a PDW being the head maid and first to respond to intruders. With all her work as a maid, a rifle or carbine must be too cumbersome to carry. A PDW is small but with just enough power to match any unwanted guest. Koa does seem more for the pistol since she works in a library where there is plenty of cover but not enough room to move. Besides, when you're running around fetching stacks upon stacks of books, wouldn't you want both hands free? Also, don't forget that the library is vast and has a great many places to hide even more firepower. Defend with the pistol to buy time to get to the rifle.
Plus, the 5.11 Tactical Duty Kilt is a nice touch.
