Ren is the national Vanguard champion and the leader of the team Foo Fighter.
Later it is revealed that he was a friend of Kai, who got mad due to a power he had called Psyqualia. That power made Ren claim that the cards of his deck were talking to him and telling him how to win every fight. Psyqualia made Ren lose himself and turn him into a selfish guy, who created the Team Foo Fighter, whose members are the best Vanguard players of the country. Kai leaves Ren when he notices Ren is taking things too far, and he goes back to his childhood town in order to run from Ren. It is also known that Ren became the best national player because he used the power Psyqualia to win. Because he has been using Psyqualia for a few years, it isn't under control and it is extremely powerful.
Ren uses a Shadow Paladin Deck which is the opposite of Sendou Aichi's Royal Paladin Deck. Instead of relying on allies to gain strength like the Royal Paladins, the Shadow Paladin Deck relies on sacrificing allies to gain strength. It also seems to boost the power of the Psyqualia user. The Shadow Paladin's Also Get Sealed Away in Season 2 and Ren and Aichi switch to using Gold Paladin's and once again he has the exact opposite of Aichi's Deck. Ren's Gold Paladin's increase field number in units, while Aichi's increase ATK. In Season 3 Ren uses the Shadow Paladin clan along with Blaster Dark Revenger. When he regains the Shadow Paladins, he begins using the Revenger sub-clan. In Season 4, Ren still uses a Revenger deck, adding now his new Legion units. Similar to Raging Form Dragon, his new ace unit Revenger, Phantom Blaster "Abyss" restands with the cost of retiring three units
Ren's strongest cards are: Blaster Dark, Phantom Blaster Dragon, Phantom Blaster Overlord, Spectral Duke Dragon, Revenger, Raging Form Dragon
Revenger, Dragruler Phantom, and Revenger, Phantom Blaster "Abyss".