Very, very, late answer but i'll do it anyways.
After Bonnie obtains a Zygarde Core, with only 2 existing in the Kalos region. Team Flare finds about this, they start to stalk Ash + Crew. Serena tries out the Master class against Aria to become Kalos Queen, then fails. Ash then meets Alain, a powerful trainer who was Pro. Sycamore's former assistant, and secretly a Team Flare member who owns a Mega Charizard X. Ash then finds Diantha, who tells some more information about Team Flare. Eventually the Kalos League rolled by, and Ash's 8 badges grants him permission to challenge in it. After making it to the finals, Ash loses to Alain. Team Flare already have taken over Z2 and enough cores to make a 50% Zygarde. Team Flare captures Ash and his Pokémon. Alain then reminds himself Team Flare is not made for Justice, but for Destruction, then quits Team Flare. He rescues Ash and then they join forces to save Kalos. Z2 Zygarde destroys Lumiose City, but Ash and Z1 10% rescued the citizens of Kalos. Mairin, Steven, and Serena found Chespie, Mairin's Chespin captured in Lysandre labs. All 3 of them then rescues Chespie and finds a mysterious rock shapes like a Zygarde which then absorbs Chespie and her energy. The rock then starts to move over to Anistar city Sundial. Olimpia tells Ash that she predicted if the Zygarde and Anistar Sundial meets, the world will end. Ash and all the gym leaders fight to stop it, but it never stopped. Squishy and Z2 becomes Zygarde 100% Forme, and destroys the Zygarde-shapes-boulder and rescues Chespie. The 2 Zygarde cores tells Bonnie goodbye, and disappeared to protect Kalos. Serena puts on a show to celebrate Kalos' protection. Ash then tells everyone he has to go to the next region. (Alola.) And there goes XYZ.
