First, I'd clarify the reason why I watched this movie is because I'm watching all the movies from the 1,000 "Box Office Mojo's All Time Worldwide Box Office". I usually don't watch movies without watching the prequels, but in the case, the prequel for this would be around 1,000 episodes of the One Piece anime and 14 other movies...so I wasn't going to do that.

So, is this movie understandable for the people who haven't watched the prequels? Basically, yes, but also, I'm sure that whatever made fans enjoy this, is precisely that, having the context for the actions happening in this movie. I can imagine having that many characters might have been epic for them, but for the rest of us, it just helps create a mess of a movie that spends too long going nowhere.

Overall, this is not a movie I'd recommend for anyone unless you are familiar with One Piece, even I'll dare to compare it with the "Demon Slayer Movie: Mugen Train" because that movie is also part of that list I mentioned, but it does a much better job at telling a story, both, understandable for the general audience that haven't watched the anime (because I haven't watched anything else from Demon Slayer previously either) and in making a movie that actually feels like a movie and not like a long episode. I don't know the general pacing of a One Piece episode, but nothing about this felt epic enough to be a movie. Should have been an episode, a season finale if you shall, but not a movie.