The newest Pokemon movie, Pokemon the Movie: I Choose You, is a retelling of Ash's earliest adventures with Pikachu. But while the movie faithfully depicts several key moments from the early anime series, it does deviate in several major ways.
When promotional artwork for the movie was released earlier this year, fans noticed that Misty and Brock had seemingly been replaced by two new characters named Souji and Makato. Fans feared that these characters were "replacements" for Brock and Misty in the new movie....and it appears that they were right.
Ash does spend most of the movie traveling alongside Souji and Makoto, all the while earning gym badges, capturing Pokemon, and searching for the Legendary Pokemon Ho-Oh. Makoto even takes Misty's place in one of the most iconic scenes of the original anime: when Ash and Pikachu fight off a flock of angry Spearow shortly after leaving Viridian City.
Gary Oak's role in the movie is also limited to a split second cameo and no reference is made to their epic lifelong rivalry.
It's not exactly clear why the movie producers chose to replace Brock and Misty with all new characters. While the cynical answer is "merchandising" (both Makoto and Souji have partner Pokemon that are a lot more popular than any of Brock or Misty's Pokemon,) the producers may have also wanted to make clear that this movie exists outside of the continuity of the show. As a reminder, none of the movies are considered "canon" (except for possibly the first movie,) so this doesn't affect the anime at all.
Misty and Brock aren't entirely absent from the movie. They, along with all of Ash's other companions through the years, appear in the closing credits of the film.
The new Pokemon movie will come out in Japan later this month and will debut in the US and Europe sometime in the fall.
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