One Piece Special: The Detective Memoirs of Chief Straw Hat Luffy
One Piece: Nenmatsu Tokubetsu Kikaku! Mugiwara no Luffy Oyabun Torimonochou
In an alternate reality world that resembles Edo Period Japan, Luffy acts as a member of the police. This is made up of two adventures: in the first, Buggy makes trouble in the town; in the second, a mysterious girl named Vivi appears (aired after Episode 253). This special contains several cameos from characters throughout the entire series. A second pair of episodes were aired after episode 290, continuing this story, as part of the New Year's special.
Seasons
One Piece Special: Adventure in the Ocean's Navel
One Piece Special: Open Upon the Great Sea! A Father's Huge, HUGE Dream!
One Piece Special: Protect! The Last Great Performance
One Piece Special: The Detective Memoirs of Chief Straw Hat Luffy
One Piece: Episode of Nami - Tears of a Navigator and the Bonds of Friends
One Piece: Episode of Luffy - Hand Island Adventure
One Piece: Episode of Merry - The Tale of One More Friend
One Piece 3D2Y: 15th Anniversary
One Piece: Episode of Sabo - The Three Brothers' Bond
One Piece: Adventure of Nebulandia
One Piece: Heart of Gold
One Piece: Episode of East Blue
One Piece: Episode of Skypiea
One Piece: Barto's Secret Room