All fighters in games powered by Exceed are cross-compatible with one another. You can battle fighters from one season of the game against any other season.
That said, balance for the game is accomplished on a season-by-season basis. So if you plan to play competitive tournaments, we recommend choosing a single season for your event.
Fighters powered by Exceed are not cross-compatible with any other game from Level 99 Games, such as BattleCON.