Neptunian is a non-binary xenogender in the celestial gender system. It is linked to the void and to a soft, celestial, masculine energy. It is never hyper masculine and it is not male-aligned, it's simply linked. Neptunian people may feel different amounts of masculine energy at different times.
The feminine equivalent to neptunian is venusarian.
Flag
The term neptunian was coined by an anonymous ask on Juparian's Tumblr blog on November 9, 2017[1]. The flag was created on the same day by Juparian[2].
The flags colors are a reference to the clouds of Neptune, as well as the void.