This looks promising for taking your games with you when you sell your Switch.
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Save data and other resources on the NX system are managed at the user level for users registered to the system. Users can register and use the system even if they are not connected to the network. A Nintendo Account is required in order to use network features on the NX. As many as eight different people can register as users on each NX system, and each user can be linked to a Nintendo Account.
Accounts Place No Restrictions on Game Design
NX accounts are purposely structured to place no restrictions on the game design.
An account does not need to be selected when the NX system is started, so you can design your application to make the selection at any time. You can ask the player to select an account in the regular way when the application starts, or you can support any of the following mechanisms to suit the game design.
For a fighting game, you can let users play in practice mode without selecting an account, and wait until they enter into the real fight mode, where scores are recorded, to select an account.
For titles that feature a collection of minigames, you can switch accounts for each try of each game. In this way, high scores are are recorded for each account.
For applications like simple party games where there is no need to store save data, you do not need to support accounts at all.
The NX system supports the simultaneous selection of multiple accounts. This means that scores can be recorded separately for each user when a number of people are playing together at the same time, like a sports game in doubles mode.
There are system features in the form of an applet which facilitates the implementation of processes in the application to switch accounts and register new users. For more information, see 5.3.1 Account Management Applet and the Account Guide.
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With the exception of system updates and a few other things, users must be linked to Nintendo Accounts to use the NX network features.
Nintendo Accounts
The chief characteristics of Nintendo Accounts are as follows. (For more information, see
https://accounts.nintendo.com/.)
The accounts are device-spanning network accounts that can also be used from PCs and smart devices.
Users can log in to their accounts using a Nintendo Network ID (NNID) or via external services such as Google+, Facebook, and Twitter.
Linking With Nintendo Accounts
A link to a Nintendo Account can be set for each user on the NX. After an account has been logged in to on the NX, there is no need to log in again (to reenter a password), aside from a few exceptions like certain errors.
By linking to a Nintendo Account, not only will users be able to play online games on the NX, but they will also be able to use services like the following to which the link is made external to the NX.
Purchasing of content (from official websites) using smart devices and PCs.
Importing resources like NNID eCash from older hardware.
Recommending friends made in non-NX applications.
Limitations on Linking
The link between a user and a Nintendo Account can be removed at any time. After the link has been removed, the user can link to a different Nintendo Account. (The operating policy might put a limit on how often this can be done.)
A single Nintendo Account can be linked to multiple NX systems. (See Fig. 1) When multiple NX systems link to the same Nintendo Account, the user nickname and icon is synchronized across systems. However, the application's save data is not automatically synchronized across systems. On the other hand, it is not possible to either link multiple users to the same Nintendo Account on the same NX system (Figure 2), or to link one user to multiple Nintendo Accounts (Figure 3).