Description
This spectral weapon, often employed by the wights and the undead, has been harnessed and bound to the realm of mortals and is now possible to wield by human hands. The weapon drains the soul from anyone its blade touches.
Notes
This weapon is much lighter almost any other.
Source
The Ghast Axe can be found in 
the Unnamed City, by looting boss creatures.
Repair
This item can be repaired with a Legendary Weapon Repair Kit.