A mysterious device crashes on planet Earth, causing a wildfire near where Gohan Son, Kuririn, Bulma, and Oolong are camping. Unable to fully save the forest, they decide to use the Dragon Balls to restore it to its previous condition. A few days later, a group of unknown warriors plant a seed where the mysterious device had crashed, sprouting a colossal tree that destroys the forest and neighboring cities in the process.

North Kaio contacts Gokuu Son and tells him that this tree is the "Shinseiju"—a tree that absorbs all the nutrients in the planet and leaves it a barren wasteland, all the while growing a mighty fruit capable of providing incredible power to anyone who eats it. After learning of this, Gokuu and his friends try destroying the tree before it is too late, but that may prove to be more difficult than they had previously imagined.

[Written by MAL Rewrite]

A long time ago, the people of Camaron Palace found themselves on the brink of destruction. Fortunately, they escaped it when Sir Aaron, the True Guardian of Aura, saved them. He sacrificed himself to stop a war between kingdoms. From that day on, a tournament is held every year to commemorate his noble deed.

Satoshi, a budding Pokemon trainer from Kanto, manages to win the latest tournament and is allowed to wield a staff said to have belonged to Sir Aaron himself. Lucario, the Aura Pokemon—who is also the servant of the True Guardian—emerges from the staff. However, remembering his last memory of his master abandoning him, Lucario runs away in confusion. 

Meanwhile, Pikachu, Satoshi's companion, is abruptly taken by a Pokemon named Mew to the legendary Tree of Beginning. Only Lucario knows the way there, but he is unwilling to trust humans after his master's betrayal. Even so, to save his partner, Satoshi and his companions must acquire all the help they need and travel to the Tree of Beginning, unfolding hidden truths from centuries ago.

[Written by MAL Rewrite]

As Goku investigates the destruction of the Southern Galaxy, Vegeta is taken to be King of the New Planet Vegeta, and to destroy the Legendary Super Saiyan, Broly.

(Source: ANN)

The story is set in Diamond Ore Country, of which Diancie is the princess.This is a country located deep underground, where the Pokémon Carbink live together in peace. The energy source of this country is a giant diamond called the Sacred Diamond, which can only be created by princess Diancie. However, the current princess doesn't yet possess the power to create such a diamond, and the current Sacred Diamond's power is soon going to run out, which would result in the end of the country. Diancie meets up with Ash and Pikachu, and set off together with them to search for the legendary Pokemon Xerneas, which possesses sacred power, but on the way, they find the cocoon where the Destruction Pokémon, Yveltal, who was said to have once destroyed life in Kalos, lies in wait.

(Source: serebii.net)