I was the middle in my birth family. Eldest sister moved away before I ever was born. 2 older brothers. 1 baby brother.
In my adoptive family I was "youngest", though that had everything to do with an age discreption clause in international adoption "as" born american on birth certificate clause-and what is supposed to be only a 1 year deviation from actual birth on the new doctumentation. I actually was middle there too. Though I was older than my traveling partner by 6 months.
In the process of divorce, remarrage and new births I was middle again.
Short answer: middle.
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"I'm sorry Katya, my dear, but where we come from, your what's known as a pet; a not quite human novelty. It's why we brought you.... It's nothing to be ashamed of, my dear, but here you are and here you'll sit."