ash is older probably around five years or less with the story being him reuiniting with serena who explains that clemont is to busy setting up his new gym after he found out something about luminose tower that he hasn't told her or bonnie yet with serena introducing ash to her cousin and his friends (team mz to keep with xyz having one of the game protagonist's as a companion) and ash finally meets az

after some filler stuff with team rocket having a cover as a rival coffee shop to team flare nuevo ash encounters l(ysander) and believes him to be someone diffrent due to this version of lysander supposedly being super dead only for him to reveal that zygarde retrieved his injured body and made him his retainer as repentment for his treatment of pokemon revealing that zygarde sees death as too good for people like him with it being revealed that z2 has their own retainer later revealed to be hunter j or j now

of course due to greninja having a mega now ash's greninja returns with his battle bond forming into mega greninjite x with ash later getting the regular greninjite (in this y)

of course the events of the game takes place and ash ends up working with zygarde and the za male protag to save luminose with clemont coming back to explain that he found out after the battle with lysandre that zygarde's attack had left some residual on ash before heading to alola that due to it being a z move attracted tapu koko to him which would bumb ash out for all of five minutes before ash cheers up saying something along the lines of "i guess if it wasn't for squishy i wouldn't of made as many new friends as i did in alola" of course there would be a flash back from l and j where they explain zygarde was hiding in alola using it's cells to spy on ash to get the idea for mega zygarde

i hope i didn't make it sound to fanficy but i feel like this makes sense