I would say its a combination of photoshop/genes/makeup. Tall women with small breasts can look quite masculine, and since asian facial features tend to remain pretty similar in males and females (speaking as an asian female), while other races tend to have more pronounced male facial bones compared to females. Ive seen other asian female cosplayers pass on well as male because of this. Im assuming the muscles and some bone structure are enhanced with makeup/editing. You can tell shes a female in her pics- shes just a very tall one with a more masculine build (by masculine i mean not curvy). As for why she identifies as agender, i would say its community influence. A trans label is a good “synthesizer” for people, especially women who dont fit the traditional feminine roles (i was roped into it because of my homosexuality and discomfort with being traditionally feminine a few years ago until i realized how idiotic it was). Its a way to make you feel like your life has a narrative purpose and every bad experience is because of you being trans (which is not the case, but it makes for a good worldview for vulnerable people). Im not saying this is whats going through her head, but this is a what ive observed in myself and others similar to me, so this is my best hypothesis. added with the fact that twitter anime communities are infested with tras, you get a lot of praise for coming out as nonbinary in those spaces. the basis of agender is not having a woman or man “feeling” in the brain- basically meaning youre comfortable in your body at the core level, because gender isnt a feeling(ironically its basically gc theory but with a trans label slapped on it).

A bad habit that gc people tend to have is assuming that males and females have to look male/female in pictures- i used to get upset at this kind of stuff too until i came to the conclusion that 1) media is easy to manipulate 2) males and females will not always be immediately identifiable & androgyny is a thing that most definitely exists. it does mess with the base gc worldview when people are able to be indistinguishable as either sex, but after a while i realized that masculine expression in women with masculine traits ≠ male & that sex is not overriden by expression.

Sorry i went on a bit of a tangent there- i hope i answered your main question at least a little. i’d be happy to elaborate on anything i said if it didnt make sense, i wrote this in one sitting on my phone lol