Journies Rewrite continued.
Leaf would be the main rival for Ash alongside Max, being revealed to have been the Bulbasaur trainer from all the way back in the OS and a friend of Ash, he's just very forgetful. Though much like Paul her starter isn't her main/ace, it's Eevee. Eevee is her strongest Pokemon and can use the LGPE moves, explained as Leaf creating those moves herself(She sucks at names lol) and being quite the strategist. She's almost like a gender swap version of Ash except she's an overall genius and not just when it comes to Pokemon. No crush on Ash, she's just a good friend and the final opponent before Ash faces Lance for the World Champion title and she ends up the Kanto Champion at the series end
Max's main is Gallade, the very same Ralts he met in AG though his starter Pokemon was a Treecko. Max aims to prove himself a worthy successor for the Petalburg Gym, thus he's entered the PWC along with knowing that Ash is participating, giving him further incentive to compete. Having won the previous Hoenn League he's quite strong and knowing Ash's strategies due to their brief time together, it makes defeating him quite the challenge! He ends up succeeding Norman as gym leader in the end
Silver, a minor rival and competing because he's traveling the world searching for clues as to who his father is. He's cold and distant but not a massive jerk(mostly cause Bede exists), eventually he discovers that it is Giovanni and he choses the Darkest Day of all times to confront him about it. Giovanni, finding out he has a son manages to snap out of it and is immediately regretful over what he has unleashed and helps Ash, the Galar League companion/Hero 2, Silver, Leaf, and the TRio end the Darkest Day threat. Giovanni peacefully turns himself in but only asks that Silver is allowed to visit him so they can catch up to which Looker agrees. Their relationship being a bit Vader/Luke like but with a happier ending. Silver's main is Sneasel cause Sneasel is awesome and deserves a big role
Bede and Marnie end up becoming two of the first Elite Four members after Hero 2 implements changes to the League after becoming it's champion; Kabu and Raihan are selected as the others
Rose helps get the Alola League properly set up as an official League
The TRio are agents of Looker, tracking down the rest of Team Rocket which is led by Archer who thinks Giovanni has gone completely bonkers giving the organization up just to spend time with his son! Keeping Team Rocket as an organization around for future sagas and stories
Hero 2 winds up settling down with Mallow a few years later; While Ash reunites with Serena and ends up going on a date with her, with Primeape, Squirtle, Goodra, Naganadel, Greninja, and Pidgeot having returned to him during the series run, it ends with all loose ends tied up and all the old companions/rivals/professors/some notable recurring characters like Korrina/Angie/Acerola showing up at a party to celebrate Ash's victory.
Ash is now 'retired' as the main character and gen 9 is a fresh start with all new characters, and the obligatory Pikachu is due to the new protagonist(If I truly had a say, it'd be a girl) being a fan of Ash's and aims to someday battle him but for now she'll work her way up much like he did!