(Prompt: The Fourth Return)
When she first left, she had sworn she'd never return.
As soon as she was able, she did.
The first time she came back, she just needed to remember the place. She needed to feel the stone under her hooves, to see the guards walking carefully through the old halls, and to catch the smallest glimpse of the one who had sent her there. She felt ashamed, needing to see her face again. There were some things that such a short time simply couldn't change.
The second time was much later, after she'd established herself in her new home. A reconnaissance mission and little more. She'd seen the signs, she knew what was coming. Even from so far away, she could feel the gathering magics. It wasn't even her home, now. Not anymore. She crept through the hallways on muted hooves, she cast an illusory glamor to hide from the prying eyes, and she made as complete a map as she dared. She had to be ready when the time came.
The third return was the one she felt was the most important.
This time she knew what she had sought was close by. It was almost too easy to sneak past the guards, her hoofsteps magically muffled and her body cloaked in darkness. The pony who had stolen what was rightfully hers slept peacefully, carelessly.
As soon as her magic lifted the crown, Sunset Shimmer knew that this Element, this power, was hers. By rights, by birth, by her own efforts, she now held the key to true power, in both worlds.
Perhaps, she had let the thrill of victory make her a little careless.
A panicked retreat and a moment of gloating later, and she felt home again. Home among the humans she'd grown to consider as much kin as any pony. The crown had slipped through her fingers, but it would be hers again soon. Who could stop her, here, in the seat of her own power?
Two days later, she had found her answer.
Twilight Sparkle, Princess Twilight Sparkle, had managed to dethrone her in the one place she felt unbeatable. Even more, she had managed to do so without the artifact. The crown, that single link to power that had driven Sunset Shimmer back to Equestria three times already, may as well have been so much worthless tin and glass.
Sunset Shimmer hadn't come to her limited power in this world by being a fool. She knew what this girl wanted, what any pony, and certainly any favored student of Celestia would want. So she summoned up her tears, she cried and pleaded forgiveness. It worked, of course it worked. Not only on Twilight but on her new friends as well. The selfsame friends that had somehow granted her the power to defeat Sunset Shimmer. Something she hadn't known before had given them all more strength than she could have imagined.
Thirty moons later, she stood in front of the statue. By now, certainly, Twilight Sparkle would have related how she'd converted. She would have told everypony how Sunset Shimmer had learned the error of her ways, and Princess Celestia, in her infinite mercy and desperate, pathetic optimism, would be hoping with all of her heart that she would return.
Like a fool, Princess Twilight Sparkle had handed Sunset Shimmer the tools to defeat her. It wasn't something to be done alone, no. Even Celestia had her friends, her confidants, her soldiers. Sunset Shimmer may be returning to Equestria alone, but she would find others to help her. She would draw on the same well of power that Princess Twilight seemed to swear by. The same power that had helped the awkward failure of a pony-turned-human defeat her.
The fourth return would be the last.