For the stories of Team Hearth and Team Fantasy, I make some changes to the stories of the games like I do with Team Lotus and Team Dawn, though a comparatively big change I make with them is just replacing the Bittercold and Dark Matter with Kyurem and Yveltal, respectively
With Team Hearth, it's similar to canon where Kyurem foresaw the end of the world and so he works to ensure that the future he saw will come to be. He's sort of become the embodiment of cold and emptiness since the original dragon split, and once he's foreseen the world will become just as cold and empty as him, he works to ensure that will come to be, and it's a sort of self fulfilling prophecy. I also want to involve Zekrom and Reshiram into the plot. Current thought is that the characters awaken the two dragons to try and stop Kyurem's plan of destroying the world, only for him to defeat both of them, empowered by the emptiness and despair in pokemon's hearts, and absorbs their power, giving him the ability to transform into Black Kyurem and White Kyurem
Yveltal replacing Dark Matter doesn't require changing the plot toooo much? I'm thinking it's almost a situation where he starts going primal, perhaps brought on by the strong amount of negativity in people and pokemon's hearts, making him go on a rampage that the hero and Mew managed to stop in the past. Like in canon, they failed to truly defeat him, only making him go dormant in his cocoon form, from which he will awaken from in the far future
