I think that Yamato will be the one joining Luffy after Wano instead of Carrot or any other girl. I know it seems crazy but hear me out.
- As we saw in the latest chapter, Yamato is a die hard fan of Oden, she admires him so much and knows things of him that almost anyone knows because of his journal. Therefore she has the dream and goal of opening Wano to the world. Having a dream to fulfill is one of the requisites /characterisitics needed to become a Straw Hat.
- You might say, “well when Wano is over, her dream would be fullfilled so she won’t have one anymore” but well, remember she is the impersonation of Oden, and also Luffy is the one who will become the King of Pirates, so what if Oden is to Roger as Yamato is to Luffy? Meaning Yamato will want to go to Laugh Tale with Luffy. Yamato has to go to Laugh Tale to learn about the true history of the world and to learn what motivated Oden to open Wano.
- Furtheromore this “dream” might be related to Ace, as we saw that she knew him some time ago and (possibly) she already knew Luffy because of him. Maybe Ace asked Yamato a favor, one that should only be done if he were to die, which he did (it still hurts). So she might have that going for her.
- There are some theories that talk about how Oda chooses who joins the Straw Hat Pirates crew (Most of them are pretty accurate). In case of the girls they seem to have a particular trait: both Nami and Robin were part of an enemy crew (Arlong and Crocodile, respectively) so, Yamato being the daughter of a Yonko, looks a lot like her being part of the enemy side (Even though she isn’t bad or anything).
- Furthermore Straw Hat Pirates members seem to join in groups of 4, 3 men and 1 girl: Zoro, Ussop, Sanji, Nami and Chopper, Robin, Franky, Brook. So far, in case Jinbe is part of a third hypothetical group, Yamato could be the girl joining in. Also she is hell strong and knows how to fight.
- Also all Straw Hat Pirates members have a tragic story. And Yamato shows all the signs of having it too. Being the daughter of a Yonko who killed the man she most admired, being beaten by her father because she told him she wanted to be like him, so they don’t seem to have the best relationship. The shackles in her wrist might be an indicator of her being held chained so she doesn’t trouble her father or his allies, and we also don’t know anything about her mother whose fate we don’t even know.
- I love Robin and Nami but it’s very clear that they aren’t as much of fighters that get hype fight scenes in this shonen series usually have so i’d love to see a character with a female body/presence get those fights and epic action scenes we are used to other Straw Hats having.
*Theory by dabarsan19