In this story, Spike's penis gets progressively longer due to an extremely lazy conceit. In each chapter, the inexperienced dragon will have a different sexual encounter with one of the very attractive mane 6. To give a basic idea of how the chapters will go:

chapter 0) just basic intro and revealing the premise
chapter 1) Pinkie Pie: very pudge. much thicc
chapter 2) Rarity: well endowed, top and bottom heavy
chapter 3) Rainbow: athletic build, but also some serious stretching around too much cock
chapter 4) Applejack: dat ass
chapter 5) Fluttershy: the fandom has been pretty clear on this one. Macro-mare-stia
chapter 6) Twilight: the special surprise inside. Wait and see.

This one will be a way for me to take a break up writing other stories and keep things fresh. Could take me quite a while to finish the whole thing.