Neptunian (also known as Merjuparian) is a non-binary xenogender in the celestial gender system. It is defined as someone who is juparian and mercurian. One could be both at the same time or they might be fluid between the two. They may feel different amounts of each gender at different times.
History
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]. However when coined the originally referred to a gender that is "linked to the void and to a soft, celestial, masculine energy". The definition of many of the celestial genders were altered by System-Lgbt is a rework of the system, to make it more consistent[3]. The original definition is now included under plutoian, and sonnian.
The flags colors are a reference to the colors of Neptune.