Film BaaD is a First World Prequel Movie.

Let's get one thing straight, it is impossible to see BAAD being anything but canon. The fact is that Toei is not recreating a Film Red. It is the peak (in terms of general reception and popularity) of what they are able to achieve under their style of noncanon One Piece films. Film Red had the first anime appearance of Gear 5 (regardless of how short it was), it was marketed with Shanks, and Ado starred as its main antagonist. It is the peak of what Toei themselves can achieve. And, even then, Demon Slayer: Mugen Train grossed twice the amount of Film Red, ~$500 million to about ~$250 million. Film Red is closer to the likes of Jujutsu Kaisen 0, ~$180 million, and Reze Arc, ~$190 million, all per https://en.wikipedia.org/wiki/List_of_highest-grossing_Japanese_films. And, get this right, box office calculations have both Demon Slayer movies, Reze Arc, and JJK0 performing above Film Red domestically, using the-numbers.com.

(Note, the number for Film Red, and only Film Red, appears to be off from its reported amount on the wiki page, perhaps it was incorrectly reported, and is actually even lower, sitting around $200 million total? The only source I could find for its ~$250 million is a Crunchyroll page, which references a tweet I am unable to find. I sure would hope it's not nearly outdone by Reze Arc and JJK0 globally!)

(there's literally no way add rows to a table)

(tossing in Dragon Ball movies, which are "new content" but canon)

(Gintama's box office does not have a specified domestic gross amount, however it only released in Japan and South Korea. And while it is popular to some degree in South Korea, I would imagine the vast, vast majority of income came from its showings in Japan. I would like to mention, though, Gintama is a fairly long series. A movie that takes place around the end of its run may have domestically outgrossed Film Red. Regardless, as it is fairly ambiguous, I will not comment further on The Final's performance.)

Point is, where One Piece is king, where “accessibility” should not be a problem, it is getting lapped by other, canon, anime movies. Nobody cares to watch a noncanon One Piece movie, not even the Japanese fans! Manga readers and anime watchers are turned away, and those who are not One Piece fans don’t care regardless. One Piece's international reach is quite literally the only reason it is not the worst performing movie. This is further driven by the oversaturation of these noncanon One Piece films, making them appear even cheaper, even less worthy of attention. Toei is clearly aware of this, considering they are willing to make a canon One Piece movie that will not feature a single Strawhat. Not Luffy, not Zoro, not Sanji, not Law, not Shanks, not a single character this series is flagshipped with. This is because the movie's canonicity more than makes up for the lack of any recognizable characters. Think about it like this, Film Red’s domestic gross relative to other anime movies is proof that Toei’s current noncanon film strategy is limiting the potential of a One Piece film. So, naturally, it stands to reason that BAAD will follow suit in regards to its canonicity after Film God Valley. Here's where the question lies, how do you make a canon One Piece film after God Valley?

The theory of it being the end of Elbaf's fight against Imu is cool and all, however that seems incredibly unlikely given how it was teased. God Valley has haki breaking through the title drop, in stark contrast to BAAD's calm sea breeze and pencil scratching as the title is drawn. Furthermore, Elbaf from the moment Imu himself drops down to the point where he is "defeated" seems like it will be quite a number of chapters, making it hard, or even impossible, to squeeze into a movie (you can expect a manga-adapting film to run at roughly a dozen chapters). And then the theory of it being the Void Century flashback is interesting, however, to be frank, I would be deeply concerned if the Void Century flashback could fit inside of one movie. Given the volume of content it has to cover, it's hard to see it going less than 20 chapters (if he's willing to commit ~20 to the "Loki" flashback I'd be willing to gamble he'd push it to 30+ for the Void Century, but let's just keep 20 as a baseline assumption). 

So how does Toei do it? In 2029, the One Piece anime will only just about be done with Elbaf, so what else is there to adapt? And here's where it gets spicy. BAAD will not be adapting more Elbaf content, it actually won't be adapting any chapters within the One Piece manga at all (as the only options do not fit), but it will still be canon regardless. And the only way to maintain canonicity this way is to be a flashback, can't have the Strawhats going on another adventure where nothing matters. And despite being a flashback, it will not cover the Void Century. So what are we left with? What is content that we can cover in a canon flashback movie that does not spoil the series as of Elbaf in the anime? The answer, the ONLY answer,  is the First World.

The First World, in concept, is massive. This essentially "Void Century" before the actual "Void Century" that we are only NOW learning exists. However, nothing about it has really been built up. Even assuming the red line was created as a result of it, it itself has never been built up as a flashback in the story. There's never been any allusion to it beyond the mural, any reason to think we will see it. Despite that, it is obviously a massively important period of history within the world of One Piece. One that would certainly have content Oda would like to show, and contain content relevant to the modern day (more on that later). It is just something that does not have a "place" in the manga to be given to us. With all this attention being devoted to the Second World, there does not seem to be any moment to squeeze in some First World flashback without it feeling incredibly out of place or forced. It would also definitely be something Oda wants to avoid in the manga, given how he is trying to streamline the rest of the series. Despite this, it is still too important to only be summarized in a chapter (I would assume some details are still briefly shown in the manga itself) without feeling like massively wasted potential. This is exactly why it functions perfectly as a canon movie. Coincidentally, it also would have been introduced in the very arc which will end in the anime right around when it is released.

Now let's dissect everything we can from both the First World teaser from the mural, and the BAAD teaser to figure out how it would be relevant to the series, or the final war in particular. The obvious stuff from the mural first, would be the giant serpent and showcasing the full extent of the Earth God fruit's power. And then for the BAAD teaser, let's list everything notable about it out.

• Sea breeze and pencil scratching

• Black backdrop

• Emphasis on the "D"

• Title "BAAD" as a whole

The first point seems to imply it will be a rather adventurous film. The second implies a possible Blackbeard connection. The third, being that this is a First World film, could imply that it would reveal the start of the Will of D. The fourth, the full name, is actually rather interesting. There seems to be a common consensus that "BAAD" stands for something, however I see no reason to believe this to be the case. One Piece Films have never been revealed with a temporary name, rather their names themselves already function as a sort of "codename". You have "Gold", "Z", “Stampede”, and "Red", with the only exception being God Valley (consider this naming convention to be further fuel for "BAAD" being brand new unique content). There is nothing out of the ordinary with the film being named “BAAD”. So, this movie is still going to be called "One Piece Film BAAD" on release, but what does it refer to? I believe, similar to "Z", it will refer to a character's name (or the main character of the movie more specifically), possibly a Sinbad inspired character. See the tweet linked here for some quick details on that https://x.com/Buggy/status/2091557629143265607. Considering the emphasis on the “D” in the title, with it being larger than the other letters, I would assume this character is a “D.” in some way. With it covering the start of One Piece history, it may even be the start of the “D.” itself. And going a bit further, I believe this character may actually be related to Blackbeard himself. As shown here, https://x.com/DawnStussy/status/2091603609503043938, BAAD contains all of the Japanese characters for Blackbeard's name. And, to make matters more interesting, it is already speculated that a First World would have strong Blackbeard connections! Following the theory of Blackbeard already possessing the Earth God fruit (for the record, I am not entirely 100% sold on it specifically being the gura gura, but I am 100% sure he will have it regardless), it is only natural that a First World movie would have strong ties to him in some form.

So to put it all together, we will likely follow the progenitor of the "D.", a distant relative to Blackbeard, and see the full capabilities of the Earth God fruit, BB's hidden power, among other things such as the possible fragmentation of the world into continents or the creation of the redline, or whatever other catastrophic event took place at the end of the First World.

• Side tangent: I believe this hypothetical Sinbad character may not have actually started the Will of D as we know it, but in retrospect will appear obvious as the first true "D.". With First World-Second World-Third World being a throughline, it is only natural for the overarching will which we are waiting to see realized to be present across all of them. And this way, the “Will of D” can still be established in the Void Century flashback, and its loose presence in the First World movie can also be tied into the grand story.

What's more, while this may be entirely coincidental, "BAAD" appears to translate to "You Are" in Somali (BB’s real world nationality, per Oda) https://x.com/kaizenhandle/status/2091482165716427200, which, if intentional, is a clear spin on "We Are", pushing the BB&BAAD connections and him as a foil to Luffy. While not his actual backstory, I would imagine the First World could provide a lot of added nuance to BB's character and his existence within the grand scheme of One Piece. And while there is absolutely nothing to suggest this, I am almost considering this hypothetical Sinbad character to be related to both Blackbeard and Luffy. Maybe even there are no BB connections and this guy's related to fucking Buggy or something, who knows. Regardless of how it plays out, the film covering the First World appears to be the only possible option.

• Worth noting, putting it through Google Translate only gives "You", however there may be more nuance to the phrase which Google Translate does not catch.

And just to acknowledge another interpretation, it is possible to argue for BAAD being a Blackbeard backstory movie, straight up. No "First World" business, but rather a normal backstory movie for Blackbeard. This is entirely plausible, but I just have a hard time believing it. BAAD as we speak is having work done on it. The problem with this is that a Blackbeard backstory is something that fundamentally cannot be exclusive to a movie, seeing a villain's life is required information in One Piece. And so, if this backstory is going to be shown in the manga in addition to the movie, similar to God Valley, Oda would need to have it already be mostly complete, despite it not even having started in the manga (apart from a few scenes with Eris in God Valley which would presumably get played back in a BB flashback). And here's the funny thing, Film God Valley itself was already having production issues! In the latest Jump Festa, Oda mentioned that the next One Piece movie was having production issues, and this took place 1 month after God Valley concluded. While this is an assumption, there is a good chance these issues arose as the movie had work started on it before the segment of the story actually ended in the manga. So if issues can form around working on a movie, of which the manga is still ongoing, what would happen if a movie was made on manga content that's still years away? Oda is a writer that will expand his world whenever given the chance, the idea of him having a Blackbeard backstory penned as of right now with even 80% accuracy is incredibly unlikely. And this is exactly why the First World works, it lives in ambiguity. We won't run it back in the manga. There is nothing holding it down, nothing that comes before it, and what comes after barely acknowledges its existence. Toei and Oda are free to work on it without worrying about contradictions, so long as the first world ends with certain things done (the hypothetical creation of the red line for example), the general plot beats do not matter. It is something that can be shown to us whenever it is done, and not spoil the events of the series as it is the deepest and farthest past in One Piece. For a Blackbeard backstory film, everything must be entirely accurate to line up with the manga's version of the story, something that would be too difficult for Oda to work with. Blackbeard's backstory could literally be the first thing following the end of Elbaf (which is something that absolutely would not happen in any world where BB is the final final villain, but let's just entertain the possibility) and I would still have a hard time believing it is what Film BAAD is about.

To summarize, Film BAAD will be canon. It does not fit for BAAD to cover the Imu fight, the Void Century, nor Blackbeard's backstory. Yet, to maintain canonicity, BAAD must be a backstory. And with there being no finished backstory past God Valley as of BAAD’s announcement, this leaves us squarely with the First World to be covered in Film BAAD, as movie-original content.