Ever since Sunset had crossed through the mirror to the human world, she knew that she was different. All the other girls were busty with curves in all the right places, while she was (by comparison) nearly flat. At first, she thought it was because she had come from another world. However, that was thrown out the window when Princess Twilight came though. Twilight's curves put everyone else to shame, making them look to Twilight how Sunset felt compared to them.

Sunset, desperate to discover Twilight’s secret, confronted the Princess directly. In response, Twilight said that the only thing that had changed recently (besides becoming an Alicorn) was the new "high energy" diet Celestia had insisted upon her. Twilight then handed Sunset a book detailing said diet.

Taking it back to her apartment, Sunset read the book cover-to-back. It talked about how Alicorns and powerful Unicorns all need high energy diets to maintain the large reserves of energy necessary to fuel their magic. Without this diet, they risk permanently stunting their growth.

This was it! This must be why she was so small! She just needed to increase her calorie intake! So, Sunset started her junk food binge, eating as much as she could each day. Heck, she could already start to see results after the very first day! Pressing onward, Sunset continued growing taller, bustier, and curvier until she passed all of her friends’ sizes and even caught up to Twilight.

Three weeks later, Sunset decided that it was time to show off her new body; one that now surpassed even Twilight.

Needless to say, they were all surprised to see the new Sunset as she walked in wearing clothes that weren’t designed for her new, curvy, Amazonian-self.