Nintendo ID/Nintendo account and Byleth

So when I started playing FEH, I created a Nintendo account after realizing that it’s not the same as the Nintendo ID I created for my 3DS years before. I eventually linked both accounts together.

I’m getting a Switch and Three Houses tomorrow. I don’t know what account the console will ask me for. Might be a silly question, but I don’t really know much about account management when it comes to Nintendo and I’d rather not screw it up.

Would whichever allow me to both get Byleth and have whatever services, DLCs and such I payed for with the other since they’re linked?

Not sure if I explained myself correctly. Thank you.

Edit: I’m going to bed soon, so I might not see the answers until 8-9 hours later.

In Feh goto Misc then Account Management, this is the email/account you will want to link your Switch through to get the free M!Byleth