Avalon from Fate/Stay Night (well, not really a weapon, but its way too powerful)

Avalon - The Ever Distant Utopia
The normal ability is healing injuries and preventing aging. Activation as a Noble Phantasm causes it to come apart in hundreds of pieces and completely protect its user from all forms of interference, a mobile fortress. Shuts (not blocks or reflects, but shuts) out all physical interference, transliners from parallel worlds, and multidimensional (multiplanar; as far as the 6th) contact; including all of the five magics. A Noble Phantasm on the level of magic. The greatest protection in the world.

Source: Fuyuki wiki