The film's story begins when Shiriri, an alien, arrives and turns Hiroshi and Misae into children. To turn them back, Shinnosuke must travel the length of Japan with Shiriri hidden in his butt. Meanwhile, Shiriri's father is moving forward with a huge conspiracy. 

(Source: ANN)

Several days after the mortal battle against Link Joker which embroils the whole world, the world has returned to peace. But Kai Toshiki faces a surprising situation. Sendou Aichi, the hero who saved the world from the invasion of Link Joker, has suddenly disappeared. In addition, everyone's memory about Aichi is lost...Almost all hints have been lost, and Kai starts to search Aichi with "Blaster Blade" and the deck of Royal Paladin, the only existing hint and the proof of their bonds. Kai is approached by fighters who call themselves "Quatre Knights". The four---Gaillard, Neve, Ratie and Sarah---are fighters with world-class power in vanguard fights. They control mysterious power and urge Kai to give up searching Aichi. What is their purpose...!? And what is their relationship with Aichi...!? Kai, with the new power "Legion" in his hand, fights to take Aichi back. Now, the war has begun! (Source: Cardfight!! Vanguard Wikia)

Ayato transfers into a new school hoping for a fresh start. Sadly for him, the school turns up to be filled with delinquents, and the most feared of them all has his eye set on him. And it doesn't help, that whenever Ayato accidentally takes off his glasses, everyone around him suddenly becomes completely smitten by him.

As humanity's war with the Neuroi—a mysterious, hostile alien race possessing weapons of unparalleled power—continues being fought across Europe and Africa, a new fighter squadron is formed. The 502nd Joint Fighter Wing, also known as the Brave Witches, operates on the eastern front, scouring the icy vastness of Orussia in search of alien invaders. However, one of the Brave Witches' members suffers severe injuries on her way to the squadron's headquarters, rendering her unable to participate in any operations. As a result, her sister, Hikari Karibuchi, volunteers to take her place. Though not possessing any special abilities or significant magical powers, she is determined to live up to the expectations of her new comrades and prove herself worthy of the name of a Witch. [Written by MAL Rewrite]