The people of the D clan are prevalent in the story of One Piece. These people are extremely important to the overarching plot of the series crafted by Oda. Simply put, those who have the D in their name are known to be the rivals of the gods who established the current world order.
The Celestial Dragons, who rule as the mightiest in the world, are the natural enemies of the D people. Sadly, through the years, the people of the D. have gone into hiding, for many reasons and, as such, there are characters in One Piece who could belong to the D. Clan yet be unaware of it.
8 Momonosuke
Momonosuke is an extremely important character in One Piece. Currently, he rules as the Shogun of the land of Wano, however, shortly before that, he was just a scared little child who wanted to take his country back from Kaido. Momonosuke belongs to the Kozuki clan, who are known to have been the crafters of the Poneglyphs, 800 years ago.
As such, Momonosuke's family has deep ties to the Ancient Kingdom. It wouldn't be a surprise to see the people of the Kozuki actually having a D in their name as well. In the future, fans could find out that Momonosuke is actually a part of the D. family as well, especially since Wano is so closely linked to Dawn.
7 Hiyori
Hiyori is a character that fans were introduced to during the Wano arc. She played the role of a courtesan known as Komurasaki in the beginning and, later on, it was revealed that she was Oden's very own daughter.
Just like Momonosuke, his sister, Hiyori, is also a potential D. clan member. Given that this family shares deep ties to the Ancient Kingdom, it is quite likely that they are secretly people of the D as well.
6 Shirahoshi
Shirahoshi is the princess of Fishman Island and a very close friend of Luffy and the Straw Hat crew. Fans were introduced to her during the Fishman Island arc and it was also revealed that she is actually Poseidon, one of the Three Ancient Weapons.
Shirahoshi has deep ties to the Ancient Kingdom and even Joyboy. As such, it wouldn't be a shock at all to see her bear the initial of D in her name. Just like Vivi, Shirahoshi could be another princess who is secretly a D clan member but is unaware of it.
5 King Neptune
King Neptune is the current monarch who rules over Fishman Island from Ryugu Palace. He is of the famous royal family of Fishman Island and his toes to the Ancient Kingdom likely go back centuries ago, all the way to the time of the Void Century. Neptune knows bits about Joy Boy, meaning the royal family has fostered great relationships with him in the past.
Neptune also harbored two Poneglyphs until recently and, currently, he has one in the Sea Forest. Given how close a relationship his family shares with the Ancient Kingdom and even Joyboy, it wouldn't be a surprise at all to know that Neptune is secretly a D Clan member.
4 Neptune Brothers
Just like Shirahoshi, her brothers, commonly known as the Neptune brothers, are also likely members of the D clan. The reason for this is the same as it was for their father.
They are from a royal bloodline of a family that has deep ties to the Ancient Kingdom and even Joy Boy. As such, they could very well have the initial D in their names, however, they seem to be completely unaware of this, if that is the case.
3 Kozuki Oden
Kozuki Oden is one of the most important and influential characters in One Piece. He played a significant role in the Wano arc, even though it was through flashbacks.
Oden is a member of the Kozuki clan and this clan, as explained already, has important ties to the Ancient Kingdom and the people of the D from the past. Oden would be one of the strongest candidates for those who have a D in their name and he might even have found this truth out when he visited Laugh Tale.
2 Amatsuki Toki
Amatsuki Toki was introduced to the fans during the Wano arc. She is a person who was born over 800 years ago during the time of the Void Century. Somehow, she found the Toki Toki no Mi, and this Devil Fruit let her jump through time. By jumping several hundred years ahead in time slowly, she found her way to the current timeline of the One Piece world. There, she met and married Oden and had two kids with him.
Toki wanted to get to Wano for her own reasons. In fact, her family, Amatsuki, was also prominent in the land of Wano once. Given her important role as a likely ally of the Ancient Kingdom, Toki could very well have been a D. Clan member as well.
1 Boa Hancock
Also known as the Snake Princess, Boa Hancock is the current ruler of Amazon Lily and the captain of the Kuja Pirates. She is one of the most formidable pirates in the One Piece world and her bounty of 1.659 billion berries goes to show for it.
Hancock despises the World Government and the Celestial Dragons sitting on top of the Red Line. She was once a slave and nobody has more reason to hate the World Nobles than her. She is more of an enemy to them than anyone else in the entire world. Oda could easily build on this and reveal in the future that Hancock is secretly a D. clan member as well.