You have to get PokeBank and PokeTransfer together - they cannot be bought seperately.
- PokeTransfer is used to migrate Pokemon from Gen V to Gen VI.
- PokeBank is used to store Pokemon from PokeTransfer, as well as Pokemon between Pokemon X and Y. Like that RS Box thing that was available when Gen III was around.
So, yes, with the assistance of PokeBank you can store Pokemon in PokeBank to transfer to your other Gen VI games.
Hope I helped. :)