The Blue Berets are a team of Obelisk Blue students organized by Axel Brodie while Duel Academy was transported to the alternate dimension at the hands of Yubel. They were used to combat the Duel Ghouls that have been transformed at the hands of a Yubel. When they tried to get to the academy's tennis courts so they could construct a portal to get back home, Vellian Crowler borrowed them to combat some Duel Ghouls blocking their way. Unfortunately, they, along with Crowler, turned into Duel Ghouls themselves. They were probably turned back to normal after Jesse Anderson used the "Rainbow Dragon" card to bring the Academy back to Earth.
The name of the name references the Green Berets, the elite special forces division of the United States Army.