Leon Soryu is a character introduced as the main antagonist of the second season of the anime Cardfight!! Vanguard, later appearing as a minor protagonist in subsequent story arcs. He is the last known descendant of the Soryu family, a once powerful and highly influential bloodline with a deep connection to the Aqua Force clan from the world of Cray. In the ancient past, his ancestors ruled the seven seas using the mysterious power known as Aqua Force, and Leon is driven by a single overriding goal: to revive his clan and restore it to its former glory, even if that means making enemies along the way. He firmly believes that the Aqua Force clan has been sealed away and sees himself as their prophesied savior, which fuels his relentless determination.

Personality-wise, Leon is calm, strategic, and intensely focused on his mission. He keeps others at a distance and shows little concern for anyone outside his two closest female friends. He often appears cold or aloof, preferring to work independently and making decisions based on logic and long-term planning rather than emotion. His methodical nature allows him to read the flow of a cardfight with great precision, a skill he once described as feeling the wind. This ability gives him an edge in battle, enabling him to anticipate his opponent's moves and strike with brutal efficiency. He is a master of the Aqua Force clan, using strategies that emphasize multiple attacks, often employing the Wave ability and the Blue Wave sub-clan to overwhelm opponents. His signature unit is Blue Storm Dragon, Maelstrom, and his Vanguard circle is indigo.

In the story, Leon first appears at Card Shop PSY, where he defeats Daigo and makes cryptic references to the wind before engaging in the Asia Circuit tournament. He enters a pact with Void, a malevolent entity from Cray, to harness its power to scatter his rivals and force the revival of the Soryu clan. He successfully defeats Toshiki Kai but is ultimately defeated by Aichi Sendou, who opposes his methods. Later, in the Link Joker and Legion Mate arcs, Leon becomes a more cooperative figure, enrolling in a Vanguard school in Hong Kong to raise the name of Aqua Force in a legitimate manner. He shows signs of personal growth, acknowledging that he no longer needs to rely solely on reading the wind and recognizing that others, such as Asaka Narumi, have changed for the better through connection with friends. His relationship with Aichi and Kai evolves from adversarial to mutually respectful, and he later takes an interest in the younger fighter Chrono Shindou, noting that the boy possesses a different kind of wind and deciding not to underestimate him. Despite his initially detached demeanor, Leon's development reveals a character who gradually learns the value of companionship and moves from a single‑minded pursuit of power to a more balanced understanding of what it means to fight for a clan.