Now that we know that “Joy Boy” is a title, I thought back to a theory that I did a few months ago.
The theory asserts that the Will of D. is actually the first initial of someone’s name. I now believe that whoever possessed the title of “Joy Boy” during the Void Century has to be someone who started a crew or clan that consisted of members that sported his first initial.
The crew or clan split sometime during the Void Century and now various people sport the “D” initial throughout the world. Whether or not Luffy or the other D’s know it. They are all collectively subconsciously supporting the original “Joy Boy”s ideals (whatever that may be). Making it what it’s known by: The “Will of D.” or in other words, the “Will of the original Joy Boy”