After the world settles down following the intense battle against Link Joker, Kai Toshiki is confronted with a startling discovery: Sendou Aichi, the renowned hero who thwarted the Link Joker invasion, has vanished without a trace, erased from everyone's memories. Left with only the clue of 'Blaster Blade' and his Royal Paladin deck symbolizing their deep connection, Kai embarks on a quest to find his lost friend. As he delves into the search, Kai encounters the enigmatic 'Quatre Knights'—a group consisting of Gaillard, Neve, Ratie, and Sarah—masters of vanguard battles with formidable abilities. These mysterious figures, wielding unknown powers, implore Kai to cease his pursuit of Aichi. What motives drive the Quatre Knights, and how do they relate to Aichi's disappearance? Armed with the newfound strength of 'Legion,' Kai engages in a fierce battle to rescue Aichi, sparking a new conflict on the horizon.