Billy debuts as a Subterra player together with Julie, where he defeated Julie with his Cycloid. He was later defeated in a rematch by Julie's Gorem.
He becomes the top tenth brawler in the world before he becomes one of Masquerade's henchmen, when he's exposed to the Silent Core. He reappears as Masquerade's henchman, along with Komba O'Charlie, and battles Julie and Shun Kazami. Although he loses, he isn't freed from the mind-control. As Masquerade's henchman, the others often make fun of him since he is the only one in double-digits and is lower-ranked than the rest of them.
Later, when Julie attempts to bring him back to his senses with a battle, he nearly sends Julie and Gorem to the Doom Dimension, but after seeing the toy he had given her when they were young, he still defeats her but right before Gorem is sent to the Doom Dimension he takes out the Doom Card. He is then freed from Naga's control and Billy explains to the Brawlers how he first met Naga.
During Masquerade's quest to strengthen Hydranoid, Cycloid is sent to the Doom Dimension. However, Cycloid (along with the other Top Brawlers' Bakugan) is later freed and reunites with Billy.
He agrees to help everyone stop Naga's minions, and slows Rabeeder's approach on the city though he couldn't completely stop her. He returns to help Julie and Nene fight Tricloid. Afterwards, he and Julie start dating.
Billy is first mentioned when Julie says that he was traveling the world to learn from famous athletes, and he was currently living in Spain. He is later mentioned to have moved to Africa to build schools, and finally appears in-person when the Vexos are hunting down the Resistance for the Attribute Energies. He and Julie tag-team against Ace, but are easily defeated. Billy's surprise visit, however, had an unexpected side-effect: it led Mylene Farrow and Shadow Prove right to the brawlers' hide-out.