Ace’s Great Blackbeard Search is the sixth mini-series created as a side story on the title pages of each One Piece chapter.
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During the course of his travels to find Blackbeard, Ace befriended the milk maiden Moda after she saved his life, and in return, he infiltrated the naval base G-2 to deliver a message to Vice Admiral Comil. During his undercover stint, he inadvertently helped reunite Moda with her parents, and acquired information on Blackbeard.
Although it was never animated, a reference to the arc can briefly be seen in the newspaper read by Crocus in Episode 381, which shows Moda with her family and Vice Admiral Comil drinking milk.
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The story can be set between the events of Jaya Arc and the events of Post-Enies Lobby Arc.