Random Thoughts.....What Are You Thinking?

Going off memory here so excuse me for any misdirection.

Lucian gave you the blade stating it was a "virgin blade" as part of your initiation and that it "thirsts for blood."

It was meant as a weapon, and seeing our first intimate interaction with the Brotherhood came with Oblivion it's not surprising we know nothing of its existence in previous titles. That said, the blade "thirsts" so my assumption would be that it was intended as a proper weapon from the start, but not necessarily expected to be as powerful as it became. It's very likely that the Blade of Woe is not a singular blade but rather any blade that is directly empowered by the Night Mother and is somehow linked to a specific member of the Brotherhood, whether it be based on skill or based on someone's role. Remember, in Oblivion the holder of the blade(the player) was put into a place to preserve the Brotherhood, when the blade reappears in Skyrim it is originally held by Astrid, who is the leader of what is the last known active chapter of the Brotherhood before being passed to you. Perhaps, using my theory, the blade is any empowered by the Night Mother that belongs to a member of the Brotherhood who's main goal, purpose, or end result is the preservation of the Brotherhood in some way.

With all that said, with our little interaction with the Brotherhood before these events, we have no idea how many previous Blade there may have been, for all we know what we know as the blade are actually reincarnation of what would have been the Mother's weapon before she became the Night Mother, or perhaps a simple embodiment of her power and the "blade" has been given to many saviors of the Brotherhood throughout its lifespan.

That all said, I wonder after the events of Skyrim what will become of the Brotherhood.