Jun is the leader of an underground fighting ring. Everyone in the underground fight respects him as a king.
Jun first appeared in Episode 36: The King of Underground Fights. He was challenged by Toshiki Kai, who was seeking strong opponents and was attracted to underground fights, a type of fight where players are allowed to cheat after hearing that their leader Jun was the strongest user of the Dark Irregulars. Jun, playing a fair game and using no dirty tactics typical of Underground Fighters, attempted to outmanouever Kai by making a bluff with Edel Rose to trick Kai into wasting his Barri and use another Edel Rose, but Kai saw through his bluff and defeated him with his own bluff with Barri. Kai then later concludes that Tetsu Shinjou is a better user of the Dark Irregulars than Jun.
Jun later appeared during the Japan Stage of the Vanguard Fight Circuit as part of Team Unknown, under the masked identity of "King Z". He goes undefeated in the stage, until his match with Aichi, who manages to defeat him due to his desire to forge his own path. Kai later scolds Jun for lecturing Aichi on finding his own path, although Jun feels that's just Kai's way of expressing how he feels.
Jun uses a Dark Irregulars deck. Unlike Tetsu, he prefers to try and Soulcharge one particular unit (Werwolf Sieger) in order to use the skill of Edel Rose as a finishing blow, with any excess soul being used to pay costs for the skills of his other units while using Demon Eater as a secondary Vanguard. However, he lacks decisive means to keep pressure on the opponent which are common in Dark Irregulars, leading to his defeat.
For the Asia Circuit, Jun uses a Dimension Police deck, revolving around the Zeal Archtype; a deck, as Aichi notes, to be full of villians rather than heroes. This deck focuses on lowering the opponent's Vanguard's power in order to force more shield when guarding, as well as gain bonuses from it with cards like Psychic Grey.
During the "Reverse" crisis, Jun challenges Miwa to a fight, with his deck still revolving around the Zeal archetype, but with new cards added, such as Original Saver, Zero to emphasize the deck's dependence on lowering power.