Before I start.. this is in no way illegal, unless I tell you to get a KSSN generator which I won't. Its your choice if you want to do it the legal way or the illegal way.
All the pictures were made by Machine on Onrpg.
Before you start, get Firefox or you won't be able to copy+paste. Which you will need.
1. Go to this website.
2. Click on the Children account registration button.
3. Select all the tiny boxes. (.-.)
4. Enter a valid Korean name and your KSSN.
It won't work unless the year is 1995-1997.
The parent KSSN must be 20 years older than the child one.
Don't type a random email. You'll need to have a valid one for verification.
Go to your mail and copy the verification code.
Don't use your username as your nickname.
For telephone just select something random from the list to the right and type random numbers.
Don't use the same mail as you used before.
Congratulations you now have a permanent account.
Writing Korean (한국어)
Now you should install NexonPlug.
You can download it here.