The more I see Marco, the more I’m convinced that he’s going to be the last member of the crew. Chapter 992 is another small confirmation for me.
“Everyone who is left is free.”
That tells me a lot about Marco. Besides just being Ace’s brother, and besides Whitebeard’s last order to him being to not let Luffy die.
And besides the symbolism of someone from Whitebeard’s crew overseeing the transition of the old era to the new, as Whitebeard predicted with his dying breath, and besides Marco being the most prominent person outside of the main players and Jinbe at Marineford in relation to Luffy and his speech that should the fail in protecting Luffy, it would be their (the Whitebeard Pirates) greatest shame, Marco is primarily there simply because he wants to be. Which says a lot about how he feels about Luffy.
Marco showing up in Wano was huge in the sense that we’re going to be seeing him for a long time now. The duration of Wano through the fight against Teach. We’re going to see a lot of development between him and Luffy, and him and the crew.
Already, the relationship between the two is built upon the same basis that Jinbe’s relationship with Luffy was, and look how that turned out. Jinbe has now joined the crew and is, in my opinion, closer to Luffy than anyone on the crew besides Zoro and then Nami.
I really think that Marco being there because he just wants to be is the best reason for him to join the crew down the road (and that’s without mentioning how that line is straight out of Luffy’s ideology).
*Theory by OEKaneki