Genderfluid
A gender that shifts over time rather than staying fixed.
A genderfluid person's gender moves. It might shift over years, over a season, or within a single week. The change is the point — it isn't indecision or a phase on the way to somewhere settled.
What moves varies. For some it's the gender itself; for others it's how strongly they feel it, or how much they want it recognised on any given day. Some change pronouns with it, some keep one set throughout.
Genderfluid people often describe the hardest part as social rather than internal: the world expects one stable answer, and gives few graceful ways to say the answer changed.