X was a Pokémon Trainer child prodigy. But now he's depressed and hides in his room avoiding everyone--including his best friend Y. An attack on their hometown by Legendary Pokémon Xerneas and Yveltal, led by Team Flare, forces X outside... Now what?

X, Y and their closest friends battle to rescue X's kidnapped Li'l Kanga from the clutches of Team Flare. Who can they trust? To protect themselves, the group of friends make an oath to follow five basic rules. Meanwhile, the secrets behind Mega Evolution unfold...

Now, what can make X smile...?