Leon first appeared at Card Shop PSY, where he fought Daigo. Leon used Aqua Force and made cryptic references to feeling the wind, but nothing else about him was revealed.
He next appeared at the VF Circuit Hong Kong Stage, where he participated as the leader of Team Dreadnought, who fought Team Q4 in the final of the stage and defeated them, and it was revealed that the "wind" he referred to is actually PSY Qualia.
In episode 90, it was explained by Leon that his family once ruled the Seven Seas due to them having the power of Aqua Force to back them up. Then suddenly the Aqua Force disappeared causing the Soryu family to lose all their power over the seas. This lead them to be long forgotten. However Leon stated that the family foretold a prophecy that a child who would be "embraced by the wind" would restore the family name and the Aqua Force clan to their former glory. He solely believes that he is that child that the prophecy has foretold.
As the winners of the Hong Kong Stage, Team Dreadnought were invited to participate in the Final Stage. However, upon being transported to the space between Earth and Planet Cray, Leon and his team opposed the other teams. Leon revealed that he had made an agreement with Void to restore the Soryu clan to its former glory. He used Void's power to scatter the others and defeated Toshiki Kai, but Leon was defeated by Aichi Sendou. When Aichi turned the tide in the battle to save Cray from Void, Leon, who had been freed from Void's influence, helped him.
He is seen again in Cardfight!! Vanguard: Season 3, and traveled to Japan to participate in the Vanguard Fight High School Circuit. He is seen cardfighting Asaka Narumi, and wins by break riding Last Card, Revonn. Leon and his team later accept a challenge that was meant for Miyaji's Cardfight Club, and he cardfights a guy who claims to have "God Hand" and such. He defeats them and meets up with Takuto, Aichi and co. for friendly fights after. He later meets Kenji Mitsusada and co., who challenged him to a cardfight, with Ali and Lee challenging Jillian and Sharlene as well. During the fight with Koutei, Sharlene and Jillian lose and get Reversed while Kenji manages to Superior Ride Dark Dimensional Robo, "Reverse" Daiyusha. However, Leon manages to harness the power of the wind and win via Break Riding Blue Wave Dragon, Tetra-drive Dragon. They proceed to un-Reverse Yuri, Jillian, Sharlene, and Team S.I.T. Genius. He is seen leaving with the twins after the entire fiasco. In the High School Circuit Finals, he is seen in the final match against Ren Suzugamori where he was overwhelmed by his Revenger, Raging Form Dragon. Afterwards, both discussed the Reverse phenomenon happening to other cardfighters.
When it becomes apparant that Takuto and Kai are the ones that he needed to defeat in order to save the reversed fighters, he arrives at Card Capital in order to see Aichi. He challenges Aichi to a cardfight but stops as soon as he rides Blaster Blade Liberator saying that his wind did not pick up upon riding his avatar meaning that Aichi has reservations about facing Kai stating that he shouldn't even try if he's in this state. Naoki, seeking a way to help Aichi in his own way, challenges Leon. Inspired by his motivation, he takes up Naoki's challenge and defeats him several times over. Though his enthusiam was great, if Naoki were to follow Leon, he would just slow him down, instead stating that he is entrusting Aichi to Naoki Ishida.
Later, during a fight against a Reversed Fighter, Leon finds himself activating his Psyqualia transporting him to where the normal Takuto is locked on Cray. Upon discovering who the fake Reverse Takuto is on Earth, he takes it upon himself to obtain a mirror to see Takuto and together storm the Tatsunagi Building with Sharlene and Jillian. Luckily, they were able to make it in time before Aichi became fully reversed allowing Takuto to assist Aichi in suppressing his Reverse with his Psyqualia. With Aichi sidelined because of the strain of such an act, Leon decides to go in with only Takuto while Sharlene and Jillian stay behind with Aichi and the others, Sharlene giving him her compact mirror so he can see Takuto.
Upon seeing the Reversed Takuto, he is transported to another area to face off against a Reversed future self who surrended to Link Joker complete with Blue Storm Karma Dragon, Maelstrom "Яeverse". This ends Leon in a situation where he had no field and no cards, but it's here where he realized that it was this kind of situation where his future self gave up hope and surrendered quietly. Through his bonds, he was able to face a near hopless situation to Break Ride to Blue Wave Dragon, Tetra-drive Dragon, increasing his power and double critical triggered to end the game. However, because Reversed Takuto used part of Leon to produce the "future" Leon, he became too tired to continue.
He doesn't care much for anyone else other than his two female friends. He is bent on reviving the Aqua Force through any means even if it means that he makes enemies along the way, for his clan who are stuck on an island somewhere. Although he doesn't show much interest in others, he does however comments on Aichi's wind being calm and that Aichi has promising skills in Vanguard. In Season 3, however, he is much more calm, collected and approachable. He also values his friends more.
Behold! Wash away all vice in the flow of furious flood. Its name is righteousness! I ride! Blue Storm Dragon, Maelstrom!
Watch! There, a crushing wave coming to clean this land of the corrupted, it is unstoppable! I ride Blue Storm Dragon, Maelstrom!
Look here! Because a dark tide is approaching and your hopes will be washed away within it. I want justice! Ride! Blue Storm Dragon, Maelstrom!
Look here! For a powerful torrent is crashing in to extinguish that flame of hope! Ride! Blue Storm Dragon, Maelstrom!
Dragon spun into existence from the warp of the wind and weft of the sea, live up to the legend in your ideal form! I crossride Blue Storm Supreme Dragon, Glory Maelstrom!
A torrent of water and air spins itself into the form of a beast ripped from your nightmares! Its coming shall herald the rebirth of my tribe! Blue Storm Supreme Dragon, Glory Maelstrom Crossride!
Tempest of water and air, spin yourself into the form of a terrible dragon! Fulfill the promise that was made to my people! Crossride! Blue Storm Supreme Dragon, Glory Maelstrom!
Level every hurdle to the ground, bring forth the glory of victory! that is your mission! Break ride! Last Card, Revonn!
Last Card Revonn! I obtain the power of Trans-core Dragon and cut through despairing destiny! Break Ride, My Vanguard!
Wielder of the demiurge, arise from the blue sea! I ride... Blue Flight Dragon, Trans-core Dragon!
Dragon spun into existence from the warp of the wind and the weft of the sea,turn into your destined form Blue Storm Karma Dragon, Maelstrom "Яeverse"!
Snowy white, swift wind! Becoming a shooting star in the night sky! Break ride! Blue wave Dragon, Tetra-drive Dragon!
Leon's new Aqua Force deck is focused on resting the entire front row (rather that four attacks and such) and break riding Last Card, Revonn to create a lot of pressure from Trans-core's Break Ride skill and Revonn's Limit Break.
He later uses Blue Wave Dragon, Tetra-drive Dragon along with cards like Tidal Assault to get him to a fourth attack to allow his vanguard to attack again. Combined with the break ride, this forces the opponent to discard up to two times and force a lot of guard.
At the Tatsunagi Tower, Reversed Takuto summoned the Reversed future-self of Leon who gave up and accepted to be reversed. The future reversed Leon, possesses Blue Storm Karma Dragon, Maelstrom "Яeverse" which gains advantages by using Link Joker's ability lock. Most notably, Maelstrom's Limit Break forces the opponent to either take the damage, which comes at them with an extra critical, or block the attack, which results in a unit getting retired.