Hi Decimus. You are a Bit confused. Bioandroids and CELLs are SPECIAL characters. And Majin Buu and Legendary are LEGENDARY Characters.
To unlock one SPECIAL Character you DON'T NEED to have a normal Character. You only need to create the Character, for example a Bioandroid, and after you must login. After login you need send 1 SMS to automaticaly unlock it.
To unlock a LEGENDARY Character is a bit more complex. You NEED to have a normal Character with more than 1kk UCs. So you create your Legendary Character and login. After login you need to enter the name and Password of your normal character, Who will be used to unlock your legendary class, that means that you will not be able to use your normal character to unlock more legendaries, but YOU CAN STILL playing normally with your normal Character. But still you need to UNLOCK your Legendary character, so after enter the name and password of your normal character you will be asked to send 1 SMS to unlock it. Is very easy
The Legendary Character will start on Noob Village with 200k of UCs and 6 special techniques unlocked (instead of 5).
Special Characters starts like normal characters.
Your normal character will not be affected at all.
Right now you can only unlock Special and Legendary Classes through SMS, i will study to use more payment options.
I hope I've been helpful