Luffy dressed as Corto Maltese, the sailor created by great Italian graphic novel author and artist Hugo Pratt. This fan art was also published in the site of Viz, the publisher of the American edition of "Shonen Jump": https://www.viz.com/fanzone#crl8-db7f96b9-f891-4f4c-a6ec-5f0b7f07cf96
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https://www.viz.com/fanzone#crl8-db7f96b9-f891-4f4c-a6ec-5f0b7f07cf96