A new Japanese trailer is out for the new pair of films as part of the 'Best Wishes' series: 'Victini & The Black Hero: Zekrom' and 'Victini & The White Hero: Reshiram'. These two movies are going to be released in Japan this July, and will allow you to download a special Victini.
In addition to the new trailer, more information regarding the plots of the two movies has been revealed. The main antagonist, Dread Grangil, has black and white hair, and wears different costumes in the two movies because in 'Zekrom' he travels in the wilderness, whereas in 'Reshiram' he travels in a tundra.
Aside from Zekrom and Reshiram being exclusive to their respective movies, it has been revealed that Gothitelle will be Dread's partner in 'Zekrom', whereas Reuniclus will be Dread's partner in 'Reshiram'. The last exclusive change announced is the presence of a different child in each movie; a girl named Sayd in 'Zekrom', and a boy named Ohdo in 'Reshiram', both of who are predicted to be linked to the main legendary Pokémon in some way.
The translation of the information posted on the Pokémon movie website has been posted below from PokéBeach:
Here's a poster of the 14th Pokémon movies:
And the following display the main characters in each movie (including the differences between them both):