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Momonosuke mentions the title "Shogun". And a Shogun is a commander in the chief of military in the Fuedal Era of Japan. But I think that in Wano, the Shogun is the equivalent or Hammock in Amazon Lily. Or moreover, the Obama of Wano.
But my question isn't who he is, but will Zolo fight him? I hope he does and I hope that the Shogun guy has one of the 'supreme grade swords'.