Cardfight!! Vanguard: Legion Mate-Hen

Aichi Sendou has saved the world, but now he has gone missing. Only Kai can remember him. Kai reunites with the Royal Paladin clan and begins unleashing a new power, the power of Legion, to help Aichi's friends remember who he is. Only by uniting them all together can they save Aichi from an unknown force that wants to destroy Aichi's memory forever.