I think Kozuki Oden was Whitebeard’s First Mate.
Let me explain how and why. First 3 things:
1- The current flashback, acording to the new time is gonna start 41 years ago.
2- And it seems that Oden have some difficult even sailing out of Wano (he needs a navigator).
3- The Rocks Pirates were destroyed 38 years ago, meaning 3 years after the start of the Oden flashback.
So, here’s what I think.
In the next 3 years in the flashback we gonna see Oden gathering his reteiners, the 9 Red Scabbards, frustraded by the fact that he is not able to sail out of Wano.
I think Oda decided to tell us about when the Rocks Pirates met their end just before the flashback because he knows that we gonna need this information.
However, one day, 3 years after the start of the story he is gonna find a man that washed up ashore in Wano. No other than Whitebeard himself (maybe he dosen’t have his Devil Fruit yet) fresh from his battle against Roger and Garp at God Valley.
Now, notice some curious facts about the Whitebeard Pirates:
1- When he died, Whitebeard had 72 years old. That means that when he fought against Roger and Garp he was 36 (72+2-38). He probably thought that was already time to form his own pirate crew.
2- No Whitebeard’s Commander seems to have more than 45 years old. Marco is 45, Vista is 47, Jozu is 42.
3- 38 years ago, when Whitebeard left the Rocks Pirates, Marco and the others were just children. I don’t doubt that they entered the Whitebeard Pirates at a very young age but they would have been only apprentices at the time.
4- I don’t think children would be the first crewmates that Whitebeard recruited. So what happened to Whitebeard’s first recruits? Died? Retired?
Well if by a chance of fate Whitebeard washed ashore of a country with a group of very powerful people thirst to leave their country… that would be perfect timing, wouldn’t? For both Whitebeard and Oden.
So maybe they met, share a drink and their dreams, Whitebeard wants a family, Oden wants to leave Wano and open its borders… Oden probably has ships, but cannot navigate them out of Wano than we find out that Whitebeard was the navigator on Rocks Pirates (I think it fits with his devil fruit powers of creating tsunamis). So they can both make a partnership and sail together. Oden accepts and became Whitebeard’s First Division Commander.
And so story goes, Whitebeard wants a family and starts recruiting unsullied orphan children to his crew and treat them like his children. Maybe Oden is the only one on his crew he don’t call son but brother.
Other things to keep in mind:
1- Whitebeard don’t want to go to Raftel (Laugh Tale).
2- At a certain point Oden left the Whitebeard Pirates to join the Roger Pirates. Everything we heard about the guy indicates that he was very honorable, so he should have a VERY good reason to leave one crew to another.
Oden was very adventurous and felt confined by Wano’s closed borders.
Probably he wanted to know more about the world, about why Wano is closed to begin with. Then he found out about the Void Century, and that the only way to find its secrets was to reach Laugh Tale. That’s the reason why Oden asks his captain Eward Newgate permission to leave the ship and join Gol D. Roger’s crew.
With the Roger Pirates, Oden reaches Laugh Tale. There he finds a secret, one that him and Roger cannot yet do something about. The Roger Pirates are disbanded. Oden goes back to Wano to try to open its boders, but then, without the protection of Roger, the island is attacked by Kaido. Oden and the future Yonko have an epic fight, with the samurai losing.
Before dying Oden says to his wife Toki to send their male child to the future, 20 years forward in time, when he would be able to “do something”.
And so the flashback ends.
*Theory by leanderbanegas
