Just a question, ZeaLitY, why are you reviving some topics?
Just a thought. I think that a Dragoon wouldn't be the one that used the masamune in the fall of guardia, unless he/she died before Radius killed Garai with the sword, he/she had to put the sword in the Divine Dragon Falls after all, unless the own sword transported there by its own means (to avoid more corruption or more blood taking).
Maybe the Dragoons in a attempt to avoid Porre invade El Nido, made an arrangement, in which the Dragoons would help Porre, and Porre would stay away from El Nido. Vipers speech may be a way to encourage the Dragoons to fight for a cause that might not be completely of their interest, but may get the army to a better position (unless that the speech is completely different than the one my memory tells me, it would be great if someone could quote it).
I stick to the point that the guy that used the masamune is someone from a different time or dimension, taking into consideration Luccas words in the letter.
My deep excuses if I'm saying stupid things, or if I'm getting out of the point.