Each time a certain number of followers is reached, prizes are unlocked. While physical prizes (That as of now include a stationery set and a T-shirt) are available only to Japanese followers, there also are digital prizes to be unlocked, and those can be enjoyed by everyone. For now you can get two twitter icons and two wallpapers from the gallery at the bottom of the post.
The next tier of prizes (that presumably will come at 50,000 followers) has also been named, and it will be a set of autographed illustrations.
Incidentally, the site itself is interesting, as it includes a ton of images, giving us another glimpse to the extraordinarily fluffy chocobos in Final Fantasy XV. Aren’t they cute?