If you could have any weapon from any fiction book ever written, which weapon would you choose?

This would be the only weapon you can ever use for the rest of your life, regardless of the circumstances.

I think I would choose the Subtle Knife from His Dark Materials trilogy. Not only for its ability to cut through any material, but especially for the ability to cut interdimensional portals.

I believe is the perfect weapon both, offensively and defensively.

How about you?