Sunbeam Sparkle is not a good pony. She might not be pure evil, but she is ruthless, ambitious, and so power-hungry that she would even aspire to usurp Celestia's throne. Worse, she succeeds in manipulating Celestia into not only surrendering rule over Equestria, but her immortality as well.
It is often said that power corrupts, and absolute power corrupts absolutely. In most cases that’s true. Many good ponies have begun with good intentions, but slowly lost their way. However, this is not always the case. A rare few virtuous ponies have the character and strength of will to resist temptation, and are never corrupted by their authority.
Even rarer, there comes a time when gaining power makes a pony better than they were before. This is one such story.
