It is number
f, as HAHAHA explains. My idea of what one piece might be is parallel to HAHAHA's idea. In the opening, from the earliest of episode, we hear Gold D. Roger saying in English translation, "Inheritance of will". Later in the series where Luffy went to see the execution place of Rogers', we find out more about Rogers' and how those words came to be. We know that he reveals his secret of his greatest tresure "one piece" in front of a crowd who came to see his execution. Roger tells the spectators his greatest treasure lies in the end of Grand Line, a sea voyage (at that time) only few had dared to take without any added incentive. I suppose Roger wanted other people to cherish the true taste of life which cannot be found in a land where peoples' lives are governed by rules and regulation necessary to sustain any civilized society. One piece is
that incentive which will drive people to leave the comfort of society to take journeys to the sea where only laws they have to follow is of the seas and I suppose Roger was counting on that. So Roger dies with a smile on his face most likely knowing that he has inspired generations of adventurer who will willingly take treacherous voyage to the seas to find his greatest treasure, One Piece. Luffy, our friendly
mugibara no otoku, is a prime example of those adventurer. So, is there truly a one piece? Hmmm..
