After Natsu gets angry, the plot might develop with other guild members trying to mediate. Happy might try to calm Natsu down while Gray could be in the middle trying to make both sides see reason. This could create a lot of comical and tense moments in the fanfiction.
Danzo could also be the one to make Naruto angry. Danzo's underhanded tactics and secrets might be exposed in the fanfiction, and if they were to directly harm Naruto's friends or the village, Naruto would be furious at his actions.
In some 'Goku Gets Angry' fanfiction, a common scenario is when his friends are in danger. For example, if Vegeta is seriously injured by a powerful new enemy, Goku's anger flares up. He then enters a new and more powerful form to fight the foe. Another scenario could be when the Earth is threatened. Maybe a villain plans to destroy the planet, and Goku gets angry at the thought of his home and family being in jeopardy. This anger gives him the motivation to train harder and find a way to defeat the villain.
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.