Since Nintendo introduced the idea of 3DS Menu wallpapers you could pay for, some first-party and third-party games have been featuring accompanying 3DS Themes as a purchase incentive, one example being the Famicom 3DS Theme that comes exclusively with Ultimate NES Remix as a limited-time offer.
With the forthcoming Japanese launch of Animal Crossing: Happy Home Designer at the end of the month, Nintendo recently revealed on the game's website that a complimentary 3DS Theme code will come included with purchases of the eShop version.
This offer is only valid until August 31, after which point the theme will become an offering you can pay for on the Theme Shop beginning September 1.
While there's no word yet on whether or not a similar arrangement will be made for the game's launch in North America, it's likely that the theme will, at the very least, be added to the Theme Shop.
To date, there are ten Animal Crossing-related 3DS Themes, which put Isabelle, Timmy and Tommy, and other favourite characters front and center on your 3DS Menu. In contrast to current offerings, the Happy Home Designer 3DS Theme features multiple characters in the same wallpaper: Lyle, Lottie, Digby, Isabelle and a sweater vest-wearing Tom Nook.