Ash Ketchum has completed the Pokémon journey that he began over twenty years ago, as he's finally become a Champion in the latest episode of the Pokémon anime series that was broadcast in Japan. The Pokémon anime debuted in 1997 in Japan, following the success of Pokémon Red & Green for the Game Boy the previous year. The Pokémon anime and video games would make their way overseas the following year, and become one of the biggest media franchises in the world.
The Pokémon anime was originally only going to depict the story of Ash Ketchum's adventures in the Kanto region. The story of Pokémon was almost completely different, as promotional footage for the first Pokémon movie that went unused shows an older Misty with a young child and Ash's Pikachu, suggesting that the film was originally going to end with a flash-forward to an adult version of Ash and his daughter. The exploding popularity of the Pokémon anime around the world caused the anime to be extended, with Ash journeying to the new regions featured in each new mainline Pokémon video game.
It seems possible that Ash is being written out of the Pokémon anime, as he's finally completed his goal of winning a Pokémon League. The most recent episode of the Pokémon anime that was broadcast in Japan showed the conclusion of the battle between Ash and Gladion in the final round of the Alola League. Ash's Pikachu was absent from the final clash, as each trainer relied on their Lycanroc for the concluding bout. According to Crunchyroll, Ash's Lycanroc won the battle, which means that Ash Ketchum is the first Champion of the Alola region.
There's been a lot of speculation that Ash Ketchum is being written out of the Pokémon anime, as the teasers for the next season state that it'll be set in every region from the history of the series. The logo of the anime is also returning to the one that was used for the first season, suggesting that a reboot was happening soon. The fact that the Pokémon video games have included fewer new Pokémon in each generation might have influenced this decision, as there's less material for the writers to work with in each season.
The recent Pokémon movies have already rebooted the story of Ash Ketchum, with the exception of the CGI remake of the first Pokémon film, and the show might be following suit. The fact that Ash Ketchum is now a Pokémon Champion suggests that his journey has finally come to an end and that the series is going to go in a new direction. It remains to be seen whether Pokémon will become an anthology show, whether a rebooted version of Ash will start over, or if it's time for a new character to become the protagonist of the series.