The Verdict: Clear Path
You are already Brazilian, so there is nothing to claim. Your first step is a current copy of your birth certificate from the Brazilian registry office that recorded your birth.
Anyone born in Brazil is Brazilian by birth, whatever their parents' nationality and however long they have lived abroad. The one exception is a child of parents who were in Brazil serving a foreign state, such as posted diplomats.
The order of documents is fixed: the birth certificate (certidão de nascimento), then a CPF tax number, then a passport from a Brazilian consulate.
If you do not know which registry holds your record, the consulate covering where you live can search for it. Tell us where you were born and we will find the registry.