Why

Ever since the death of her two friends, Applejack the super-bucker pony will not endure it. Not a single bit. Apple Bloom did not notice the abnormal behaviour in AJ until she fell sick. With The Yellow Disease.

Usually, Applejack will always have a very big appetite, and will never leave the dining table without having at least five apple pies. But today, AJ only ate three. The next day, she ate one. One the day after that, she could not even eat without having to rush to the toilet.

One day, AJ could not even get out of bed without Apple Bloom's help. Bloom had to drag her off the bed, and then flip her over onto her stomach, then straighten up her four hooves. Even after that AJ still cannot walk on her own.

As AJ's condition got worse and worse, Apple Bloom's teacher Cheerilee also started to give a lot of homework for the school foals, so Bloom had lesser and lesser time to take care of AJ. AJ's yellow mane became her yellow body. In the end, AJ died a painful death.

There was a huge crowd at AJ's funeral. Granny Smith was wailing like nuts. Big Macintosh was sobbing quietly for his beloved sister. Even Cherry Jubilee was there, although she was not a close relative of AJ's huge family.

Again, the Crusaders gathered at a quiet alley near the funeral, and Sweetie Belle sighed. "Why are everyone dying so quickly? Is the Yellow Disease really so powerful?"

"Crusaders, we've got to find a plan, or just a very fundamental idea, so as to stop or just slow down the speed of the Yellow Disease spreading. We've already lost half of the elements. If we don't do anything, everypony will die." said Scootaloo.

The three fillies clapped hooves, and they temporarily put aside their cutie mark crusading. Now their mission is to protect the rest of the Elements from the Yellow Disease......but how? What could three fillies with blank flanks do?