[Question] What else can I do?

I have beat the game and rebattled the league and completed my Pokédex and yesterday caught Greninja 7 star. Is there any left to do? I even bred Greninja and have his 2 prior evolutions. Don't want it to be over.

Did you finish all your classes by passing their final tests? Did you do all the little events with your teachers and rivals at the school?
Did you also catch Charizard and Cinderace during their raids? If not you could try trading for one of their line.

Otherwise I think all that's left is either hunt for HA Pokemon in 3 stars and up Tera Raid dens, or shiny hunt.
There is currently not much to do once you've finished the game.

I am not sure how to do the Shiny hunt but would love to get a Charizard! Do you have one to trade?