The Poké Bank was one of Game Freak’s best ideas in recent times, neatly sidestepping the trading issue that has existed in these games for years. No longer do you have to pass Pokémon through a few games via a lengthy and inefficient process, they can simply be uploaded via one game and downloaded via another (with some caveats). The problem comes with support for the service; Pokémon Sun and Moon took a couple months before they were compatible with the Poké Bank.
That apparently won’t be an issue with Pokémon Ultra Sun and Ultra Moon, as it’s been confirmed that they will be adding support for the service by the end of the month. It’s unknown why the original releases were so slow to get support, but fortunately it won’t be long until you can import your favorite team.
