Name of this anime

I watched the anime and I want to read the manga but I don't remember the name, in the story people live in cities that moves constantly and the Mc was one of the strongest in his city but bc of his illegal duels (to win money for the orphanage he grew up in) he was exiled and he move to this other city as a normal student but the council president knew about his past and made him transfer to the special/combat (? ) division. In the story cities will have battle against each other for the limited resources, in witch you have to take down the flag of the opposite city. THANKS IN ADVANCE