Feline Fluff has a problem. She doesn't know how to deal with stallions. Living in a shop filled with cats does't help her sanity, not that there's much of it to help. Read as Feline becomes a better pony through difficulty, and failure.
Derpy doesn't understand why ponies don't accept her. After losing everything she ever loved, only the power of friendship, and love, can she become understood, and accepted as normal.