User blog comment:Mckrongs/Monster Hunter 4 for the Nintendo 3DS/@comment-5505638-20120901063828

Ironically enough, I have read something about this weapon concept on a fanfiction (yes, a fanfiction) before they even released these. The idea in the story was that a hunter had heard of a monster that could not be defeated by any specific weapon. Wanting to prove people wrong, he faced it.

He barely escaped.

As he lay dying in his pain-induced insanity with a good portion of flesh stripped off of him, an epiphany struck: If no one specific weapon was able to kill it, why not make every weapon into just one? As he lay on his last breaths, he made his ideas into blueprints on just how to make such a weapon. He then encased it into an envelope made of his own torn skin and sealed it with something that would only allow it to open when the individual who had it needed it most.

This is just from my recollection, so a couple things might be off or missing.

Other than the fact that the author was from Indonesia and had it in English (with a few transliteral errors, of course) which makes me think they leaked it early via a fanfic, I think that THIS is the said weapon described in the story that they have revealed.