Here are the listed anti-Yamato arguments I can collect so far. Most of them sound ridiculous, but some are pretty good arguments. Let me summarize again:
1. Goroawase DF pattern
2. She doesn’t have specific role
3. She is introduced too late
4. Luffy calls her “Yamao” instead of “Yamato”. She is on the same level as Law & Kid
5. Her DF is Wano’s guardian deity
6. She read Oden’s journal. She knows too much especially about One Piece
7. She is too strong. She will break monster trio dynamic
8. She doesn’t interact with any other Straw Hats, only Luffy and briefly Franky
I’ve posted the counter-arguments for about 5 of them. But I really want to know what pro-Yamato’s counter arguments regarding the arguments above.
1. May or may not be relevant. Oda revealing the existence of the idea in an SBS may be an expression of his intent to not follow it but merely plant the seed in the readers mind so that it makes it harder for readers to predict what he is going to do going forward. Following such an idea limits how Oda can craft his story.
2. Yes, no expressed ship role yet. But neither did Jinbe until WCI (helmsman was only a possibility until it was confirmed). At present, Yamato's ship role could be many things, including a role that seemingly appears inconsequential at this point to the journey of the Straw Hat Pirates. Until we get further focus on what exactly Yamato can do beyond fighting (and making Vivre Cards), certainty remains lacking:
- Den den Mushi-tuber/Marys-tuber - taking Oden's journal idea further by using state-of-the-art technology to create a visual recording of the journey to share with the world (the
cakeOne Piece is no lie)
- Vivre Card craftsman - why does such an item exist? Does the history of Vivre Cards relate back to the Ancient Civilisation? Can the application of Vivre Cards be expanded on like how science expands on the use of Devil Fruits (Chopper, Caesar, Queen, Vegapunk)? In the absence of a Log Pose route, would the presence of a Vivre Card craftsman be helpful?
Yamato does have a potential story role going forward.
3. Why is this a problem? And late in regards to what? The story? The saga? The arc?
4. Why is this a problem? Luffy calls his crew members by their name when they become members. Set-up has been laid by Oda where Yamato will become part of the conflict between Kaido and Luffy. Kaido knows that if he wishes to break Yamato's spirit, he first needs to break Luffy. And Luffy is aware what Kaido represents to Yamato's freedom. When the emotional stakes are at their peak, that may be when the pay off happens e.g. climatic moment in the Kaido battle or at the end of the arc.
5. The Wano Arc has been building up toward Momonosuke severing Wano from its history and directing it toward a path leading to the future. Wano's borders will be opened and with such an act, it will become part of the world once again. Wano will become a country that will be significant in the arrival of the "Dawn".
The development of Yamato having a Devil Fruit representing a Guardian Deity of Wano as per Kaido, could exist because it has been set-up for Momonosuke to eventually sever such a shackle for Yamato (and help Wano move on from the past). Just as Ace helped sever Yamato's shackles toward accepting their desires, just as Luffy severed Yamato's shackles by removing the explosive bindings and defeating Kaido (will happen), just as the Samurai (Daimyo) severed Yamato's shackles by cutting the chains in the Sacred Cave and believing in Yamato, Momonosuke will sever Yamato's shackles by removing the notion of duty. At such a point, Yamato will have freedom to choose what to do. Yamato's Devil Fruit could be argued to have more to do with Momonosuke's story than keeping Yamato in Wano.
6. Oden's journal is not a spoiler. Oden understood the importance of what was at stake and would not have included too much information in the journal.
Considering Oden discovered the secrets of the world along with Roger, he would be aware of why the information the ancient civilisation knew wasn't openly shared and instead kept behind the text of the Poneglyphs that not anyone could read.
Just as Roger didn't reveal the secrets of world during his execution. Just as the rest of the Roger Pirates didn't reveal the secrets of the world. I don't believe Oden would have revealed the secrets of the world either verbally or through his journal.
Roger and Rayleigh knew the secrets of the world needed to be uncovered naturally through the journey. Oden would have felt the same which would have extended to what he wrote in his journal. Oden would have omitted the complete story of the Ancient Civilisation and only covered the brief details of his adventure and their discovery. The fact that Oden was resolved to opening the borders of Wano once he returned, he knew just like Roger what was at stake. I genuinely don't see Oden risking the Roger Pirates efforts by revealing all the secrets of the world in the journal.
Oden included just enough information in his journal to help guide the next generation (such as Momonosuke and Hiyori and those who would inherit Joy Boy/Roger's will) to completing what "Joy Boy" started.
7. How is Yamato's strength being measured? Because it is obviously not directly against Luffy, Zoro and Sanji. To compare the efforts of someone who fought Kaido for 20 years against someone who faced Kaido for the first (Zoro) or second (Luffy) time requires more reflection than a direct one in regards to the events taking place. Yamato learned Kaido's attacks and his body became familiar with his attacks beating after beating. Of course Yamato would have faired better against an opponent he fought for twenty plus years when compared with someone who only faced Kaido for one or two times. Lets also not forget that in contrast to what Kaido said, when he was fighting Yamato, Kaido didn't intend to kill him, Kaido was only attempting to physically, mentally and spiritually break Yamato until Yamato was submissive to his commands.
Zoro is offensively stronger than Yamato based on the damage done to Kaido. And with Sanji's body undergoing a metamorphisis, his abilities and capabilities have increased.
Rather than renounce a character of Yamato's strength joining the Straw Hat Pirates, readers should rejoice, as it would mean Zoro and Sanji get be highlighted more in battle.
When you think about who the Straw Hat Pirates are going to face when the Elbaf, Vegapunk, Laugh Tale, and World Government stories come into focus, it appears obvious why adding a strong character to the Straw Hat Pirates seems justified, appropriate and necessary.
Yamato's addition in this very arc does not throw off the balance of the Straw Hat Pirates military might. It does not make them overpowered or the arc less exciting, rather it allows for tougher opponents to come to the forefront and enhance the thrill of the events. Proceeding arcs will function the same even if someone with Yamato's strength joins the Straw Hat Pirates.
As for the general crew dynamics, Yamato joining may give more focus on Robin who has been criminally kept in the background for far too long. Yamato joining could also help add relevance to Jinbe presence’s in the crew. Yamato has been “imprisoned” for twenty years and there is no way that such a reality and past would not create emotional and mental scars within them. Jinbe has experience with being among former prisoners (Tiger, Koala and other Sun Pirates) so if Oda wanted it explored, he could have Jinbe help Yamato with any trauma and mental anguish they may have – Jinbe has helped Luffy through his mental trauma in the past. Robin after having met Koala (and being enslaved herself) may also have some insight in Yamato’s situation and be able to assist.
8. If there ever was a character who could join the Straw Hat Pirates with limited interactions with any of the Straw Hat Pirates outside of Luffy, it would be a character themed around Kozuki Oden, a character who joined the Roger Pirates with only interacting with Roger.
With that said, Yamato may yet get further interactions with the Straw Hat Pirates based on where he is currently heading - toward the Onigashima Skull dome.