That stowaway excuse again? This is not good excuse for being absence throughout Wano arc. It would feel ridiculously cheap that anyone could do that. Fans would feel terribly upset rightfully so. That she had not done anything up until this point or change the tide of war. As well most her personal conflicts have already been resolved by non strawhat members. So, there is no incentive for her to continue further with them.
It would feel unrewarded because she did not show signs of importance within the arc like earlier strawhats were throughout the Grand Line. Carrot is already friends with half of the crew why can’t she asks luffy for herself? She does not have to sneak onboard their ship to get notice because that would cheapen the finalization for the last strawhat because she had not conducted anything throughout wano.
What about Vivi sneaking on board huh? There is bit of difference between Carrot vs. Vivi’s situation. Even though Vivi weaker by comparison. Vivi situation has simply been talk about ever since Dressrosa and throughout Reverie arc. Her family being the traitors to the world government could lead to interesting storylines down the road. Vivi is there as for her own protection than again you can have her be there be working under the Revolutionaries.
I am still for Yamato joining the the crew.
Yamato has abandoned momo not just once but twice in the same raid in order serve for Luffy sake. Yamato is a person is very impulsive and impatient character she does not want to babysit Momo. She has said, five times already of leaving this place going out to sea get much stronger than she is now. She has never said anything about wanted to serve under Momo. Throwing the explosives cuffs that bind her to this island and defeating the person who had hinder her progress. It means to us as fans that she has enough motivation set sail with the strawhats to help them further on their journey. Knowing about Luffy hidden goal and ambition could lead to some interesting interaction down the line. The fact that her father called her out always being alone, she had no friends, anyone who shows her compassion wind up dead. It does remind us as fans how the other strawhats were like in their own personal lives. In the raid both Jimbei and Sanji say Luffy he should reserve energy against main threat at hand meaning in future battles Luffy will solely focused on the captain. If he does lose the fight again. His crew members must hold off that person off for the time being until he recovers. When wano arc is over wano practically it is going to be under Luffy’s territory from now on. Which means Luffy allies will protect for him. The enemies there going to face from now on are going to be much stronger than the earlier one. That is how one piece usually goes. So why not take strong fighter who you free from their predicament. This arc also centers around a character who will manage carrying on oden’s will. During the oden’s flashback Roger’s does say there will be someone will surpass them. Ace could not do it because he is dead. Momo still has a mind of child and none of the nine scabbards are interested in going on adventure. So, why not take someone who is an outcast, someone who could continue oden ideals with them and someone who has been close off from rest of the world for 28 years. It also relates to one of Luffy’s other goals of gathering crew that could surpass Shanks one day. There you go
throughout wano.
Stowaway is not an excuse, it's the most probable option for Carrot joining the crew. This can be said because of how Carrot was reintroduce with the story, how Oda managed the Mink during Oden's flashback, the character arc of Carrot and her characterization. Again, this is not "an excuse", this is what is the most LIKELY to happen. Period.
Secondly, it wouldn't feel cheap as this was prepared throughly by Oda multiple time as a gag and a likely possibility. It would only feel cheap for those who don't read or don't know the story. Remember that we are not talking about Carrot integrating the crew as a member of the strawhat, but as a simple crewmember, a stowaway. Carrot will need something more after that.
Thirdly (and for the LAST time) Carrot's conflict has NOT been resolved yet. You don't get a conflict resolve only because the guy you hate has been beaten, that's cheap writing (and cheap understanding), you get your conflict resolved when you confront your own weaknesses and beat them. For Carrot it has not happened yet.
Fourth, Carrot is not an asker, it's a taker. This can be said because of her characterization. Carrot was not depicted asking she always takes the road she WANTS to take. So if Carrot wants to go on the Sunny, it is very unlikely that she simply ask Luffy. Like all the strawhats, Carrot is a free spirit, she will make her way up there by herself.
The whole point of the stowaway action, is the surprise it will bring. So no, it is not a question of being rewarding, it's a question of stayin in CHARACTER.
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FIFTH.. Vivi sneaking anboard enter in conflict with Vivi's characterization. Vivi is a respectable princess, and she will most likely ask for Luffy to join (or be forced to join them if it needs to happen). Remember, you can't just applie what you want on a character, it has to be in synch with the development and characterization of said Character. That's why:
Franky was forced to join, he would not ask (too proud), and not sneak in
Zoro joined by respect and consequences
Nami was first teaming up
Usopp had to be told that he was part of the crew
etc.
Each character have their own characterization. If you don't take those characterizations and development/character traits into account, you will just theorize a cheap situation.