We don't have enough details to know who the writer is. It could be a new writer trying to make a name for themselves with this off - beat concept, or it could be someone who just wrote it for their own amusement or to share with a small group of like - minded people.
Maybe it's a work of fanfiction within a particular fandom that uses the idea of 'America being called fat' as a plot device or a central theme. It could be part of a story that involves characters from different nationalities or entities interacting with this personified 'America' and making remarks about its 'fatness', which could then lead to various sub - plots like self - discovery, change, or conflict for this 'America' character.
It could be about a character named Anerica who is bullied or taunted for being fat, and then she goes on a journey of self - discovery and self - acceptance.
It could mean that America is seen as something like a fictional or made - up construct in some ways. Maybe its history, culture, or political situation is being compared to the often wild and unconstrained nature of fan - created fictional stories.
There could be the bullies who call Anerica fat. They might be the typical mean - girl or - boy types, who are insecure themselves and pick on Anerica to feel better.
Often, there could be a theme of adjustment. Tails having to adjust to his new, larger body. This could involve things like how he moves around, his confidence levels, and how he interacts with the world around him. It might also touch on themes of body image, as he might struggle with how he looks now that he's fat. There could also be a sense of adventure where he has to overcome new challenges because of his size, like fitting through small spaces or being slower in movement.
Maybe in the 'sonic gets fat fanfiction', Sonic discovers a new type of power - up that gives him super strength but as a side effect, it makes him gain a lot of fat. He then has to learn to control this new power without sacrificing his speed and agility. He might go on a journey to find a way to reverse the fat gain while using the power for good.
Dr. Eggman would be a likely main villain. He might be the one who devises a plan to make Sonic fat, thinking that it will slow him down and make it easier for him to be defeated.
One way to find 'tails gets fat' fanfiction is to ask in relevant forums. There are many Sonic the Hedgehog fan forums out there. Explain what you're looking for in a polite post. Other fans might be able to point you in the right direction. They may have read some great 'tails gets fat' fanfictions and be willing to share the links or titles with you.
The team would likely be in a state of shock at first. They've come to rely on Steve's leadership and strength. His injury could make them more cautious in their actions. They might hold back on some missions until Steve is better.