For Serena, we don't know nothing official for now... but I don't think that she will go to Alola. I think that we will have a new female main characterSerena will go in alola?can ash greninja in sun and moon?ash Pikachu journey finish in XYZ?
Can't wait to see old characters return after years!!
In the new opening for the anime in Japan, it has been confirmed that Kiawe, Sophocles, Mallow and Lana, supporting cast in the Pokémon Sun & Moon anime will make appearances in the new series soon. This marks the first return of any previous supporting cast in Pokémon Journeys and the first returning ones aside from Brock & Misty since Dawn appeared in Pokémon Black & White. We'll provide more details as they come.