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I don’t think someone can be fire born at birth my theory is that passionate humans that die to lava in the nether come back like phoenix’s from ashes sapnap some how found himself in the nether and before bbh could find him he being a small baby fell into a lava puddle and died but came back as a fire born that’s why I believe that jack manifold is fire born it would be a good explanation for why he came back to life after dying to lava in the nether