Ancient Kingdom = Clan of D
Clan of D stands for Clan of Dreamers
D’s have the ability to bring their dreams to reality, their dreams become Devil fruits.
Only the D’s can make Devil fruits it’s an inherited ability. Think of it how some people are born with conquerors haki and you either have it or don’t it’s not something you can acquire.
20 Kingdoms and maybe even the rest of the world feared them for this ability but only the 20 strongest nations (as we can see Alabasta and Dressrosa were part of the 20 kingdoms, they are some of the strongest and largest nations we have been introduced too) rose to challenge the Ancient Kingdom.
The Ancient Kingdom was made up of many different races but they were all D’s and almost if not all of its citizens had Devil fruits. The Devil fruit tree was in the ancient Kingdom so not anyone could just come in a take a devil fruit.
The rest of the world feared what would happen if they decided to essentially take over the word by force. I think the ancient kingdom was a good kingdom not a war hungry nation but the possibilities scared people and the desire to have devil fruits of their own and get fantastic powers of their own.
Maybe haki wasn’t always a think maybe the 20 kingdoms came up with it and maybe even the 6 powers as a way to combat devil fruits? The addition of haki was a surprise to the Ancient kingdom and being an advanced peaceful kingdom they weren’t accustomed to war and were easily overwhelmed. But they were too “kind” to use their technology or scientific weapons on the 20 Kingdoms.
Everything is really a possibility but Devil fruits clan of D? Then we don’t know what the D stands for and now with this concept the devil fruits are Dreams I think that’s what the D stands for and the reason the were whipped out is the world feared the power of the D’s ability to manifest dreams into reality and they sought out the devil fruits for themselves. The Devil in devil fruit just goes along with the D initial and the propaganda spread by the WG.
I don’t think the Void history is going to be black and white I think it will involve alot of gray and that the original celestial dragons weren’t all bad but acted out of fear and once they obtained devil fruits for themselves that’s when they decided to turn on another potential danger in the Lunarians and with devil fruits they were actually able to combat and defeat them taking over the red line.
Defeating this scientifically advanced civilization and then the “Gods” of the red line went to the 20 kings heads and they started to see themselves as gods and that’s when Vivi’s ancestors decided to separate themselves from that.
That’s just my theory on it I haven’t heard or scene anything similar to it but I just wanted to put it out there.
Theory by Silver Fang Bang (https://www.reddit.com/user/Silver-Fang-Bang)
