The official website for the I Choose You film shows Ash dressed in his original anime clothing, kneeling next to Pikachu in a field as Legendary Pokémon/Pokémon Center Kyoto mascot Ho-Oh flies across the sky, evoking a similar sight which Ash witnessed at the end of the first Pokémon TV episode nearly two decades ago.
The callback is entirely intentional, because the trailer for the I Choose You movie shows someone, ostensibly series protagonist Satoshi/Ash, donning the cap the Pokémon Trainer wore in the first arc of the Pokémon anime.
The 20th Pokémon movie will bear the subtitle I Choose You.
All of this seems to suggest that the I Choose You movie is going to be a retelling of the beginning of Ash’s journey to become a Pokémon Master.