The first half of the second season of Cardfight!! Vanguard G series.

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)

Taking place after a three-year time skip, the series will follow Shindou Kurono, Kiba Shion, and Anjou Tokoha as the new protagonists of G. Kurono uses the never-before-seen clan Gear Chronicle, which brings together the destinies of these three toward an impossible future, an impossible self signifying 'Generation.' (Source: vanguardus.blogspot.com, edited)

Taking the world by storm, the card game Cardfight Vanguard has influenced many to integrate card games into their everyday lives. Players of the popular game are called cardfighters, and they frequently battle each other in card shops. The game has inspired many people, one of which is the quiet and timid Aichi Sendou who is often ridiculed and bullied by his peers. Whenever he feels down, he takes a glance at Blaster Blade—a legendary rare card given to him when he was young—and gains the motivation to move on with his life. However, one day, school bully Katsumi Morikawa notices Aichi's treasure and snatches the card away from him. After a turn of events, Aichi soon discovers that the card is now in the hands of Toshiki Kai, a cardfighter who has become the strongest in town despite having only recently arrived. To make matters worse, Kai refuses to return the card unless Aichi defeats him in a cardfight. Much to everyone's surprise, Aichi rises up to the occasion. As he musters up his courage and pictures himself winning this decisive battle, Aichi begins to find his way into the adventurous world of Cardfight Vanguard.