Board Thread:Skyrim/@comment-112.208.96.173-20140927112006

The Keening kills anyone who touches it without the Wraithguard its because it has the ability to absorb lifeforce of their soul upon touching the hilt. The Last Dragonborn's case is different because he has a soul like that of a dragon. The Keening's effects are nullified because of it and therefore Wraithguard is no longer needed. This means that the Last Dragonborn made to wield it for reasons unknown and perhaps the Keening is actually a part of a weapon that has been created a long time ago before it has been shattered into pieces. 