What if Gen 9 was about a microscopic region that gets captured by the new villain and they harvest the miniature energy from the region to shrink cities from other regions and capture them.
A portion of the game will involve you visiting the shrunken cities from different regions and working with notable gym leaders and characters to unshrink their city.
After freeing the other cities you finally get the ability to grow to the size of the normal world and face them to free your region and the box legendary from the clutches of the villain.