One Piece Green: Secret Pieces is the fourth databook.
- Names and sketches of Whitebeard's Allies.
- The "Anime's 8th Anniversary Suplex" letter written by Eiichiro Oda. This small article was published in the magazine One Para (Volume 3), and then in One Piece Green on page 347.
- In this letter, Eiichiro Oda explains many things about the mascot, Tony Tony Chopper.
- Holds the combined full stories from the cover story arcs.
- Reveals sections of Oda's sketchbook and early One Piece.
- Origins of characters' names.
- A few Mugiwara Theatre stories.
- A new subdivision of the first half of One Piece manga in sagas is given:
- Dawn of the Adventure Saga (Chapters 001-095)
- Grand Line Challenge Saga (Chapters 096-216)
- Gold Land of Sky Saga (Chapters 217-318)
- Straw Hat Pirates vs. World Government Arc (Chapters 319-441)
- Ghost Island Adventure Saga (Chapters 442-513)
- Intrusion! The big prison Saga (Chapters 513-550)
- History Greatest Summit War Saga (Chapters 550-597)
- Curiously, Chapter 550 is divided up between the 6th and the 7th saga
- The subdivision is different with the manga site's official one.
Front cover under flap.
Back cover under flap.
Early CP9 concept sketches, and fight match ups.
Early designs of the Straw Hat crew.
The original 8th Anniversary Suplex letter.