Bandai-Namco is adding cross-play support for its two 3DS fighters later this year in Japan!

One Piece: Great Pirate Colosseum and Dragonball Z: Extreme Butoden, Bandai Namco’s Arc System Works-developed fighting games for 3DS, will each be updated in early November to add cross-game battle support, Bandai Namco announced.
This will allow users to battle each other no matter which title they own. Goku can battle Monkey D. Luffy, for example. Or Vegeta can fight against Nami. Cross battles will support both local and online play.

Source: Gematsu