In the Ryugu Kingdom arc, the name Joy Boy was first introduced based on the writing on ponegliph discovered by Nico Robin. The Ponegliph told a story directed by Joy Boy to a Mermaid who lived in a century of emptiness where he promised to bring the entire population of Fishman Island, fishmen to live on the surface, build Noah, and explain that the Mermaid was one of three an ancient weapon capable of destroying the world named Poseidon.
During his lifetime, Joy Boy failed to fulfill his promise, but the promise is still held firmly by the Ryugu royal family where they believe that there will be someone who will be able to keep Joy Boy's promise by keeping Noah's ark and keeping the story between the poseidon relationship and Joy Boy to the outside world. In One Piece Chapter 915, Gol D. Roger after finding the last island and named it Laugh Tale or Raftel, hopes to live in the same era as Joy Boy. Then, Who is Joy Boy, let's discuss the facts about this one character.
Fact 1:
He was an adventurer 800 years ago, so he could meet with Poseidon, leave the Pluton Ancient Weapons in the Kingdom of Alabasta and establish good relations with the Kozuki clan in the past where we know that only the Kozuki clan can make and sculpt Poneghliph in One Piece.
Fact 2:
Joy Boy is the most hated by 20 kingdoms who currently form the World Government as a result of his knowledge of ancient weapons, Poseidon, Uranus, Plutons.
Fact 3:
Joy Boy is the person who left the treasure on Laugh Tale Island in the void century.
Fact 4:
Joy Boy is a person who bears the name "D" just like Luffy, Garp, Dragon, Teach, Rocks, Roger, Ace, and so on. It is known that some poneghliph also told stories about the history of the name "D" in the past and their enthusiasm is still continued by those with the name "D".
Fact 5:
Joy Boy was the king of the Ancient Kingdom feared by the heavenly ancestors who now lived in Marijoa.
Fact 6:
Joy Boy has ambitions to create All Blue, where we all know that the Grand Line is now separated by the Red Line. By destroying the Red Line using Ancient Weapons, the seas of East Blue, West Blue, North Blue, and South Blue will mix and all the fish will gather in one ocean called All Blue.