To the best of my knowledge we've never had an incidence of someone who can alter their gender AT WILL in real life, so pretty much any pronoun I chose to use would be incorrect. I just threw whatever came to mind at the wall. Pick whatever you feel works best.
EDIT: I suppose genderfluid works (and now that you mention it, was probably what was used in the actual text, I honestly forgot). Genderfluid character, then.
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"Art bearing high similarity to a large majority of art found on Tumblr".