Now there are only two opponents left, as 3 out of Big Fives are defeated. The mysterious boy Noah's next target is a trio of Tristan, Serenity, and Duke. Still wondering in the virtual realm, they open a door that floats above field. Behind the door is a place that is much like a factory. There they find Big 4 waiting. He is Ota Soichiro the former manager of Kaiba factory for military equipments.
Big 4 challenges the three to have a 3:1 duel with him. Tristan and Duke defend an inexperienced Serenity and declare to have 2:1 duel. But since Big 4 is after all three bodies, he does not allow Serenity to withdraw from the game. It is then Serenity accepts the challenge and joins the duel.
Big 4's deck-master is "Mechanic Sergeant." Using its special deck-master attack called "Backup bombardment," Big 4 attacks each player and reduces their life powers by 500 per machine-type monster card that has discarded from the hand. In addition, Serenity becomes an easy target since she doesn't know the rules to duel…