Primary antagonist of the first season and leader and co-founder of Team Asteroid (originally known as "Team FFAL4 (Foo Fighter Apex Limited 4)" in the Japanese version), which consists of about 500 members branched off in different teams. Ren is a powerful cardfighter who has a very sadistic personality in which he enjoys mentally tormenting his opponents. He looks down on anyone he faces, claiming that there is no point in trying to beat him since his victory is assured. Ren is also one of the first people revealed to have Psyqualia, which allows him to foresee his victory in his fights. As seen in flashbacks, Ren was an innocent and polite albeit absent-minded guy who used to be on the same team with Kai, until his Psyqualia awakened and soon corrupted him into who he is now. Along with Kai, Ren also adds "the" to his move declarations and announces "Final Turn" when he is about to deal the finishing blow on his opponents. He also seems to know when another person has Psyqualia, noted when he meets Aichi at Card Shop PSY to give him the Shadow Paladin deck, which he also uses. The deck, as shown in Aichi's fight with Kourin, acts as the polar opposite of the Royal Paladin deck, which sacrifices allies to gain power instead of working together. Ren's, and Aichi's for a certain time, ace cards are Blaster Dark and Phantom Blaster Dragon. He later gains Phantom Blaster Overlord.
Ren returns in the second season as the leader of New Team Asteroid (referred as "Team New AL4" in the Japanese version). He also uses a Gold Paladin deck like Aichi but with a different trump card, Spectral Duke Dragon. Ren sometimes borrows other people's decks to try and find a possibly better-suited clan to use. Ren's personality has reverted to his former innocent childlike self in spite of Takuto appearing and reawakening Ren's Psyqualia during his and Aichi's fight during the Seoul Stage of the Vanguard Fight Circuit.