Gender Reincarnationism is one feels a deep connection to reincarnation and feels as though they themselves had a past life. That connection to their past life has a lot of affect on their gender. Those who feel connected to being male in their past life may identify as a trans male in their current life. Those who feel connected to being female in their past life may identify as a trans female in their current life. The same thing also goes for any nonbinary identities, anybody who felt as though they were a form of nonbinary identity in their past life, may identify as a nonbinary identity in their current life.
This is not exclusive to only human past lives. A person could've been a male dragonfly, a female cat, or a plant in their past life. One does not need their past life to be that of a human in order to use this microlabel. The only requirement is to have some form of connection to having a past life and feeling as though the gender in that past life affects your current gender.
One does not necessarily need to believe or feel connected to reincarnation. One could feel as though they had a past life and not believe in that thought, but still feels as though it has a effect on their overall gender experience.
This is also not a religious term. Anybody people of any religion or non religion are allowed to use this term.