What we know as "One Piece" is not just something we can obtain. "One Piece" is the codename of a plan from the Ancient Kingdom 900 years ago. This plan was the destruction of Marijoes and Fishman Island. These places lay in the middle of the world. Destroying that spot will link all the sea's together, creating "All Blue", and give true freedom to the world. The will of D is something that only a small group of people have, people who have this D, have inherited the will of the Ancient Kindom's beliefs and so they try to carry out their plans to make the world free again. Roger, dying from a disease, could not fullfil his role in this. So he started a new age of pirates. Hoping for someone to inherit this will again. Here is where Luffy shows up. A major hint is the 100% accurate future visions from that mermaid lady. Luffy will destroy Fishman Island because he needs to destroy Marijoes to connect the world. - Luffy will become the Pirate King because he did all of this, destroyed the World Government and giving the world freedom to sail wherever they want to. - Nami can draw a map of the entire world easily now. - Chopper can find any kind of medicine now. - After this adventure Ussop will be a brave warrior of the sea. - Brook can finnaly go back to Laboon very easily. - Franky can sail all sea's with Sunny. - Robin has discovered all this for luffy, so she found out about the real history. - Sanji has now found "All Blue". - By this time Zoro is already the strongest swordsman in the world I think. The story of One Piece has always followed a certain formula. - Someone has a dream / something to achieve - Time passes by, the original dreamer dies. - Someone new comes and inherits the past dreamers will, and maybe reaches it.