[in this context, Rin is who Len was before transitioning]

You’re “Rin‘s” older sibling, college age to be more specific. Which meant you spent a lot of time in your dorm and less time at home. But finally, since it was Christmas break, you decided to head home for the time. You figured that it would be nice to spend your Christmas with your family, like you always have. But you weren’t expecting to go home and find that your little sister was now your little brother.

You had just come home and put all your stuff in your room. “Rin” hadn’t come to see you yet and your parents were being oddly suspicious when you brought it up. So you decided to go up there yourself.