Registering a Nintendo Network ID on Wii U lets you join the ever-growing community on Miiverse, jump into exciting online multiplayer action, download a vast range of content from Nintendo eShop and more.
From the user selection screen, select the user to link to the Nintendo Network ID. Please note: User accounts without a registered Nintendo Network ID display a grey background behind the Mii character. User accounts with registered Nintendo Network IDs have blue or orange backgrounds behind their Mii characters.
Select "User Settings".
Select "View/Modify User Information".
Select "Next" or press the A Button and enter the user's password.
Select "Link a Nintendo Network ID" then choose one of these two options:
Select "Create a New ID" to create a new Nintendo Network ID
Select "Link an Existing ID" to use a Nintendo Network ID already created on Nintendo 3DS
Follow the on-screen instructions to complete the process.