Obviously, Italy itself would be the main character. There could also be other European countries like France and Germany. They might be the ones causing Italy's anger, or they could be Italy's allies trying to calm it down.
One possible plot could be related to environmental issues. Italy is known for its beautiful landscapes. If other countries are not taking proper actions to combat climate change which is also affecting Italy's natural beauty, Italy could get angry. It might start its own initiatives and try to persuade other countries to follow suit, leading to a story full of challenges and cooperation.
There could be original characters created specifically for this fanfic. These new characters might be the source of Sakura's anger. For instance, a new villain who has targeted Sakura or her loved ones. Or it could be a rival who constantly undermines Sakura, causing her to be angry. Additionally, characters from other related series might make cameo appearances if it's a crossover - type fanfic.
Cell - like characters are often antagonists. Since Cell was such a major foe in the original series, new versions of Cell - like beings could be created in fanfiction to make Gohan angry. They might target his loved ones or the Earth itself, provoking Gohan's rage.
The parents, Mom and Dad, would probably play a significant role as they are the ones who could potentially bust Candace. Also, there could be some minor characters from the original show like Perry the Platypus. He might be involved in some way, perhaps he accidentally reveals Candace's plans which lead to her getting busted.
There could be her family members. Her mother might be the one constantly checking on her temperature and making sure she is comfortable.
Well, it could be a terrifying experience for her. Maybe she'll face danger and have to find a way to escape.
Germany would likely be a main character. He has a close relationship with Italy in the original series, and Italy's transformation would surely affect their dynamic. He might be confused at first but then grow to accept and support Italy in this new form. Another could be Romano. As Italy's brother, he would have a very strong reaction to Italy's change. He might be overprotective or even a bit jealous if other countries start to show too much interest in his now - female sibling.
The main character is Steven. Alongside him, his father Greg could be a crucial character. Greg has always been there for Steven in different ways, and he might be the one who can reach Steven on an emotional level during his corrupted state. Lion, Steven's magical pet, could also be a main character. Lion has the ability to travel through dimensions and might be able to find a solution to the corruption in some far - off place.
It could be the leader of the red team. Maybe he gives the caboose the toughest and most dangerous tasks without any proper recognition.
There could be her parents. They might play a role in encouraging her to get braces or helping her take care of them. For example, they could remind her to brush her teeth properly with braces.