A story in the same vein as My Little Dashie, but not a carbon copy.
Awoken in the middle of the night by a mythical creature sitting on his doorstep, a man's life is drastically re-arranged by the sudden entrance of Princess Celestia. Struggling to accept things he couldn't ever think possible, he'll have to make a decision about what's worth changing his entire life.
(Note: I added the "Alternate Universe" tag because I imagined this being a reversed-roles universe where Luna is the big sister and banishes Celestia, rather than the other way around.)

When your life is as dull a gray as the world that surrounds you, the mundanities can make it all seem meaningless. Sometimes all we need is a little color -- or six -- to reintroduce us to what truly makes life worth living.

*6-16-2017 Edit, added Rainbow Dash tag because it triggered knighty.*