When Ryu returns to pay homage to his deceased mentor, Gouken, he is tormented by disturbing memories of his master's killer. In a quest to become a true martial arts master, Ryu sets out to hone his street fighting skills and to deliver himself from the haunting legacy of the Dark Hadou. But the ultimate test of his new power can only be accomplished through one last fateful confrontation with his arch-nemesis, Gouki (Akuma).

In the new, whimsical era of Battle Spirits, cards have become scattered across a colorful galaxy, enticing all "card questers" to duke it out in search of the strongest cards. Rei is a flamboyant wanderer who is obsessed with being on top. Accompanied by a small dragon named Mugen and a talking robot named Salt, the self-proclaimed "Number One Star" regularly engages in card-gaming mischief through flashy battles. One day, Rei meets Raira and Rikuto April, both of whom seem to have clues on the whereabouts of the "ultimate" Battle Spirits card. Together, they embark on a quest to search for the card, clashing with many vibrant personalities along the way. Soon, their adventure catches the attention of the Guild, wily villains who are also set on obtaining the Ultimate Battle Spirits. In contending against the Guild, Rei's status as number one is put to the test—an endeavor that will slowly unveil secrets regarding the fate of the universe. [Written by MAL Rewrite]

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)

Kujou-san no Do-S Soudanshitsu Anime-ban short anime specials bundled with the Blu-ray and DVD releases of Ore ga Ojousama Gakkou ni "Shomin Sample" Toshite Gets♥Sareta Ken.