Well, a butt expansion MLP fanfic could be a fanfiction where the writer has come up with a really unusual plot. Maybe it's some kind of magical or strange event that causes the butts of the MLP characters to expand in the story. But it's not a very common or mainstream type of fanfic idea within the MLP community. It might be more of a niche or even a joke concept that someone thought up.
There are very few, if any. The MLP franchise is known for its positive messages, friendship, and cute characters. A butt expansion fanfic goes against this in a rather odd and inappropriate way. Maybe the only 'positive' could be that it shows the creativity (albeit in a strange direction) of some fans, but overall it's not a positive addition to the MLP fan community.
One reason could be genetics. Just like some people are genetically predisposed to having a certain body shape, some men inherit genes that lead to a larger buttock area.
I'm not entirely sure as it seems like a very specific and rather odd concept. 'MLP FIM' stands for 'My Little Pony: Friendship is Magic'. But 'rarity butt inflation fanfic' sounds like a made - up and strange fan - created story that likely involves some sort of comical or perhaps inappropriate (if taken too far) inflation concept related to the character Rarity. However, without actually reading it, it's hard to say exactly what it's about.
Once upon a time, there was a furry little fox. It had a big, fluffy butt. One day, while running through the forest, its big butt got stuck between two trees. It wiggled and wiggled until it finally freed itself and learned to be more careful while running in narrow spaces.
Once upon a time, there was a mom who had a rather large butt. She was very self - conscious about it at first. But one day, when she was at the park with her kids, she used her big butt to break the fall of a little boy who was about to tumble off the slide. After that, she realized that every part of her body could be useful in some way.
Once upon a time, there was a little girl who had a big butt. She was always self - conscious about it. But one day, when she was at a dance competition, her unique body shape gave her an advantage in balance and rhythm. She ended up winning the competition and learned to embrace her big butt as a special part of herself.
Once upon a time, there was a princess who was known for her large and beautiful dress. People often thought her dress made her butt look big. One day, she went on an adventure in the forest. As she walked through the thick bushes, her big dress got caught. But she didn't panic. Instead, she used her intelligence to free herself and continued her journey with grace.
It's not popular at all. Popular MLP fanfics tend to be those that explore the core themes of the show, such as the magic of friendship, the challenges the ponies face, and their growth. 'Rarity butt inflation fanfic' is a very niche and rather unappealing concept to the general MLP fan base. It goes against the more common and positive types of stories that fans usually look for, so it's not likely to be something that has a large following.
The plot could involve a big - butt animal, like a hippopotamus. In the story, the hippo is always left out of the 'thin - bodied' animal games. But one day, there is a flood in the jungle. The hippo's big butt helps it float better than the other animals. It then uses its strength and big butt to rescue the other animals one by one. This makes all the animals realize that everyone has their own unique qualities and they should not be excluded because of appearance.