Sie; an intensive repetition of a gender-neutral subject, often used to indicate exclusiveness of that person as the only satisfier of a predicate.
Hir, themself; gender-neutral third-person singular object of a verb or preposition that also appears as the subject, coordinate with gendered himself and herself.
it; used to intensify the subject, especially to emphasize that it is the only participant in the predicate
The door itself is quite heavy.
it; A thing as the object of a verb or preposition that also appears as the subject