Ash has been a helpful friend and hero to all people and Pokemon alike with everyone that he's inspired and changed the lives of and everyone he's saved as well. He's already a Poke Monaster, as the flower blooming to match part of Mezase's lyrics shows. he just doesn't realize it because he's far more humble than the cocky brat who left Pallet Town ages ago. And even after being a Master, he'll just keep going to new dreams and new adventures until the very end. His dreams and aspirations will never really die and he'll always keep getting better as he makes more friends and changes more lives while they also change his own despite him still being that hopeful trainer at heart. Every part of that, even the smallest moment, is all a part of him being a Pokemon Master. That's the whole point of his journey, of "Pokemon Master" and what MPM was hammering in. Maybe if people weren't trying so hard to make everything about what they want, they'd realize what things actually are and know the only ones who set them up for anything more were themselves.
Ash's journey isn't over, but our time with him and all of his friends and rivals is done for now. Time to close the book and start the next one until a new volume suddenly comes out one day.
Bye for now, Ash. Thanks for everything, it's been fun. See you again someday, Pokemon Master.
Here's a song I'm sure everyone here has heard at least once.