It’s Burning Crusade Timewalking week, which means eligible Demon Hunters can earn the Warglaives of Azzinoth appearance from Black Temple.
I’ll Hold These For You Until You Get Out requires you to kill Illidan during Black Temple Timewalking after completing the Warglaives of Azzinoth achievement and rewards Arsenal: The Warglaives of Azzinoth.
The arsenal lets you transmog the legendary warglaives from Black Temple. However, to obtain it, you must first earn both warglaives the regular way on a single character that can equip them.
Note that Warglaives of Azzinoth achievement credit is not account-wide and you must own both first before you enter Timewalking Black Temple and kill Illidan.