This is a new category of quest that is unlocked once you find the first piece of one of the quest weapons. You most likely unlocked it when you picked open the chest in the Caldera Gun Works and found the hilt for Wave Dancer.
(2.7.2) Weapons > Soul Caller
You find this hilt in a chest on Antigua, and you find the blade in...
(2.7.3) Weapons > Stormwind
You find the hilt for this special weapon in a Level 60 Chest on the beach on the Isle of the Dead. You find the blade in a chest on Maracai, and when you assemble the two you get a weapon with stats of 45-60 and 15 Slashing Weapons. Not as good as Wave Dancer but still a decent blade! Once you repair the two parts you complete this quest!
(2.7.4) Weapons > Wave Dancer
The hilt to the special weapon Wave Dancer was acquired in the locked chest in the Caldera Gun Works. Once you have it that flags this quest, and you need to find the rest of the weapon in order to repair it to make a superb blade! The blade itself is in a chest on The Isle of Thieves, and once you have it you still need to repair the blade which means learning Forging from a Smith.