Mii changed on my 3DS

So I have had my 3DS for about three years now as well as a Nintendo Network ID. My little brother was recently given a Wii U and being the kind older sister I am, set it up for him on my Nintendo ID.
Well, about a week later, my Mii on my 3DS changed to the one he has on the Wii U instead of my own and I can't seem to change this. My personal settings are still the same, yet my name and character has changed.
Any help is much appreciated, thank you.
Best Answer
Only one Mii and username can be associated with a Nintendo Network ID at a time. If it is changed on one device, it automatically changes on the other. You have two options:
- Use the same Mii and username as your brother
- Create a new NNID and associate it with the Wii U. You can find instructions for this on Nintendo's website.
Good luck! Feel free to ask in the comments if you have any problems.
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How do I change my default Mii on 3DS?
Complete these stepsCan you change your personal Mii on 3DS?
Choose Mii from the list of Mii Characters. Select "Yes" to confirm. Note: This is the only Mii you can change - you can edit your personal Mii, but you cannot delete it or switch it for a different Mii you have created. (It actually warns you about this when you create them, and also in the manual.)How do I change my NNID Mii?
Complete these steps-NO LONGER WORKS- How to ACTUALLY Change your 3DS Personal Mii (Not Just Edit)
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Answer 2
You need to create a seperate Nintendo Network ID per person, otherwise this will happen.
If he hasn't played on the Wii U yet, you can just delete his profile and then create a new profile with his own Nintendo Network ID. After that, you should be set your own ID's Mii again.
If he has already played on it, then you have a huge problem now because deleting the profile will also delete all the save data. You'll need to contact Nintendo and ask if they can unlink the Nintendo Network ID without deleting the profile so that you can assign a new one. Nintendo customer service can be really frustrating to deal with though :-(
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.