جَاءَ زَيْدٌ نَفْسُهُ: nominative subject and nominative emphasis.
رَأَيْتُ زَيْدًا نَفْسَهُ: accusative object and accusative emphasis.
مَرَرْتُ بِزَيْدٍ نَفْسِهِ: genitive noun after bāʾ and genitive emphasis.
These teaching examples show that emphasis tracks the case of its referent; the pronoun stays referentially fixed.