I think people are jumping to conclusions fast
How did Luffy's Journey Start? With Brother Trio
One living in a Kingdom, One living in a Village & One living in a Mountain with Bandits
When Ace Died, it was shown over & over again that Luffy Inherited Ace's Will
But who ended up having Ace's DF? Was it Luffy? No
It was Sabo
Joy Boy was Confirmed to have Ability same as Sun God Nika
And Joy Boy was Confirmed to be from Ancient Kingdom while Nika is from Elbaf (Huge Mountainous Area)
So Joy Boy isn't Old Era Luffy as People think He is, He is probably Sabo of Void Century
While Nika was Ace of Void Century, and We still have a Third Character to Discover (Someone from a Village)
Joy Boy becoming a Pirate is Reference to Sabo leaving his Kingdom to live in Gray Terminal where He basically identified as a Pirate & think of it as Mini Version of Grand Line, but Sabo's Journey didn't Last Long and He was forced back inside his Kingdom
The 20 Kings are probably from Ancient Kingdom, the War between them & Joy Boy was an Internal Conflict, just like Sabo was against the Cleansing of Gray Terminal, while the Nobles (Representing the OG Kings here) Supported it
However, who was the actual Villain of that Flashback? It was King of Goa Kingdom himself
And who was assigned to Destroy Gray Terminal, it was Bluejam Pirates who were Defeated by Ace & Bandits.
In other words, Joy Boy vs 20 Kings wasn't the Main Battle, the actual one was between Nika & Elbaf Army vs whoever was Unleashed by Ruler of Ancient Kingdom
This means that Imu is just one of those Nobles who wanted to Rule so badly & ended up Succeeding to some extent, and is there such Character in Sabo Flashback? Yes, it's Sterry (Sabo's Adopted Brother) who became Ruler after the actual Royal Family Mysteriously Died
(But as Hinted by Kuma Flashback, They wanted to become CDs, and either They were Killed for Insisting or They actually did Succeed & They faked their Deaths)
The Actual Villains of Story whom Joy Boy truly wanted to Disappear Forever are Ruler of Ancient Kingdom & whoever He unleashed upon the World who both Disappeared & will one day Return (Bluejam was Tricked by King of Goa Kingdom & only realized it after He already started the Destruction of Gray Terminal)
We already heard of these Two Characters, They were mentioned in Fishmen Island Arc as "Sea God" & "Vander Decken", their Legend clearly indicates that Vander Decken was used to Unleash a Storm upon the World by Sea God who as Name suggests was probably Title He got for being Ruler of Ancient Kingdom
Another thing to mention is that Bluejam claimed all the Treasures of Gray Terminal, but his Treasure was stolen by Sabo & Ace cuz They wanted to use it to buy a Pirate Ship, this actually matches with Vander Decken as his Legend is exactly like Davy Jones & there is a Song in Fishmen Island Arc that confirms Vander Decken is considered "The Richest" who claims all the Treasures.
So that's what Joy Boy took in his Journey as a Pirate & used to create One Piece.
OG Kings answered to this Sea God (Hence why Mary Geoise Holy Knights are called God's Knights, that's who They serve)
Imu on the other hand is the Traitor, He is the one who wants to Rule instead of that Sea God, that's why He does it in Secret, He is like the Devil who turned against God
