In addition to the multitude of NES games obtainable as furniture items, the player can also acquire a blank NES (a blank Famicom Disk System in the Japanese release). On the surface, it appears to be nonfunctional, and interacting with it simply brings up the text "I want to play my NES, but I don't have any software." However, in 2018, dataminers discovered that using the item actually causes the game to scan the GameCube's memory cards for externally installed NES ROM data. By downloading NES ROMs onto the memory card, it's possible to play them in Animal Crossing via the blank NES, including titles not obtainable in the base game.

Six years later, Twitter user Gloomyfates discovered that this is a carryover from the original Doubutsu no Mori, in which the feature was officially utilized by a sweepstakes in Nintendo Dream magazine in which up to 30 contestants could win Controller Paks containing Ice Climber (which is not present anywhere in the N64 game's data). This indicates that at one point in development, Nintendo planned to hold similar events for the GameCube version, distributing additional NES games via memory cards.

The ROM loading function additionally enables one to patch NES ROMs after they are loaded, which can be used to install mods for Animal Crossing itself via the memory card.