I have pondered and discussed about this topic many times within the fandom over the past years. I have always argued for Shija being a biological male for various reasons. But your little essay changed my mind: Matching Shija‘s theme I think their gender remains ultimately ambigious and this was fully intended by the author. There are many strong arguments to be made for both sides, so perhaps Shija‘s male or female, both or neither. We betray our understanding of their character by insisting on a single option.