No, I'm talking about what Kamina says in episode 8 (omae o shinjiru omae o shinjiro, 'believe in you who believes in yourself'), not what he says earlier (omae o shinjiru ore o shinjiro, 'believe in me who believes in you'). I understand the confusion, though.
Of course there's no need to use 'jibun' for a sentence like "I, who had just X, then did X." What I'm talking about are sentences like "I did X to myself who had just X", in which the reflexive would be used instead of just using a first-person pronoun twice. in other words, 'watashi wa jibun o shinjiru,' I believe in myself, vs. 'watashi wa watashi o shinjiru,' I believe in me.
in other words, the issue isn't the relative clause, but the fact that the subjects of both clauses are the same thing. Again, this is confusion that probably arose because we were thinking of different Kamina lines.