One Piece will end with the Straw Hats finding One Piece which is a time machine. By this point Enel is a crew member. They then learn from Alvida, who is one of the Yonko now, that she saw Enel at Loguetown when Luffy was saved by lightning. Enel says he wasn't there, he's never even heard of Loguetown. Nami and Robin both suggest that they must have used One Piece to go back in time to save Luffy. They must fulfill the loop, so they travel back to Loguetown and Enel saves Luffy.
However, Luffy stretches out as he and Enel go through the time portal. Enel was fine and ended up where they intended, but Luffy's body is so stretched out he's covering hundreds of different moments. This sends him back even further in time, ripping a hole in timespace as it does so. This literally wipes out 100 years of history. The void century is not simply missing from history books, it was destroyed from existence by Luffy. He continues even further back in time until he finally comes to rest in the distant past. He's near a village that reminds him of his hometown, although it turns out it's not the same place - it's 1000s of years prior to that. There isn't even a WG.
Time montages forward and Luffy eventually has a wife who gives birth. She suggests using Luffy's middle initial in the baby's name as well, and Luffy says he likes that idea, they should name all their children that. Eventually, we get to the point that Luffy is dying of old age, he's now about 250 years old. The mayor of the town, the new mayor, comes around and asks Luffy to write his will. His children and grandchildren, great granchildren etc are all gathered around, all have a D initial. He writes out that the only thing he will leave to them, the only thing he really has, is One Piece. Not only does he leave it to those gathered, he leaves it to all their future children too. This is the Will of D. We then see a distance view of the village and the words "The Island of Raftel" come up in the frame.