Ace’s Great Blackbeard Search is the sixth mini-series created as a side story on the title pages of each One Piece chapter.
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.
The story can be set between the events of Jaya Arc and the events of Post-Enies Lobby Arc.