This story is told using 2nd person perspective. In other words, the story is from your point of view. Genders and physical descriptors are left mostly ambiguous, allowing you to self insert/"fill in the blanks" with whatever suits your fancy.

You are small, having shrunk from a known virus a few years back. One day, your friend comes to you with a question, more of a favor really. They have a fantasy, a long desired sexual act that can only be done between a shrinkee and someone normal sized, and they'd like your help to make it a reality...