Isn't it obvious? Usopp's weapon's will be imbued with Haki.
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Oh and two years is enough time for Geko Moria and/or Vegapunk to revive Ace as a puppet to potentially stop Luffy.
I've read quite a few posts...but I'm surprised no one mentioned this:
Don't you think Moria's disappearance means the return of Zombie or Vegapunk Ace type return sometime down the line?
