My main inspiration lays in Season 1, episode 20 "Green isn't your colour". If you care to rewatch that episode it may help you understand this story better.
This story is my attempt to explore one possible path a relationship between Rarity and Spike. How would it start? How might it become more serious?

Be warned, there is a small trample scene, but not entirely out of character if you care to watch the aforementioned episode.