After upsetting longtime fans of the Pokémon anime with removing Misty & Brock from the re-telling of the first season in the movie
I Choose You!, Misty & Brock are returning in the current season of "Pokémon: Sun & Moon" for a 2 episode special. Currently, Ash has been living in the Aloah region attending Pokémon School and completing Island Challenges instead of the normal formula of facing the Pokemon League and Gyms since 1997. He returns to Kanto for a "school project" and will eventually face against Misty & Brock in a nostalgia filled battles.
Looks like Brock will be battling with a Mega Steelix that evolved from the Onix that he had since 1997. While Misty will be fighting Pikachu with her Mega Gyarados that she caught in the side series "Pokémon Chronicles" in 2002. We might be visiting Professor Oak's lab and Pallet town where Ash's previous Pokémon reside along with the Exeggutor meeting its Alolan version.
The trio split after their Johto adventure in 2000 when each of them had a different goal to pursue. The original trio reunited when Misty ran into Ash, Brock, and new companions May & Max while on their Hoenn adventure in 2003. Brock held on as Ash's companion until 2010 with the end of "Pokémon: Diamond & Pearl" exploring the Sinnoh region. Both of them only been mentioned through word of mouth, memories, and a few side episodes without Ash.
The 14-year reunion will be broadcasted on September 14th and 21st in Japan with an English dub and broadcast most likely, later on, this year.