Today, Nintendo announced a new downloadable 3DS companion app for their upcoming Pokemon X and Y versions. It's called Pokemon Bank, and it's used to store in-game Pokemon in the cloud.
Pokemon Bank allows you to store Pokemon in online boxes — 100 boxes, meaning 3000 Pokemon in total, which is far more than the game's in-built total storage capacity. The software will also let you transfer Pokemon from the previous generation (ie. Pokemon Black & White and Pokemon Black 2 & White 2) into X/Y, with a feature called "Poké Transporter."
Nintendo also revealed that since the service will require constant maintenance, players who want to use it will have to pay an annual fee.
Pokemon Bank launches in Japan on December 25, where it will cost ¥500, about $5, annually. No release date, or pricing information, has been released for regions outside of Japan yet.