Since I'm not familiar with this novel, it's possible that there are prophets or seers as main characters. They could be the ones trying to understand the gods' anger and communicate it to others. Or perhaps there are brave warriors who are either trying to fight against the wrath of the gods or are on a quest to make the gods calm down.
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.
The main character is the 'last angry man' himself. Around him, there could be family members such as a wife or children who either support or are at odds with his angry nature. There may be neighbors who are affected by his actions or words. And perhaps there are colleagues or people from his workplace if the story has that aspect. There could also be a local community figure, like a priest or a community leader, who tries to mediate or influence the angry man's situation.
One character that could work well with an angry Loki is Doctor Strange. Strange is used to dealing with powerful and unpredictable entities. He could either try to manipulate Loki's anger for his own purposes or try to help Loki come to terms with it. And of course, Sif. She has a history with Loki and her loyalty to Asgard could put her at odds with an angry Loki.
I don't have enough information to say who the main characters are. It could be a tough - as - nails Aussie bloke who's had a rough life and is out for revenge. Or maybe a group of characters, like a gang of outcasts in an Australian town.
Batman's allies such as Commissioner Gordon could be involved. Sometimes Batman might be angry at Gordon if he feels that the police force is not doing enough to support his fight against crime. Also, other members of the Bat - family like Batgirl could be part of the story. Their actions or decisions might trigger Batman's anger. For instance, if Batgirl decides to take on a powerful villain alone against Batman's advice.
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.
The key characters are definitely the birds and the pigs. The birds, like the Red bird which is kind of the basic angry bird, are the ones on a mission. They have different colors and abilities which make them unique. The pigs, on the other hand, are the troublemakers. They took the eggs which set off the whole angry bird saga. They try to hide in their flimsy or sometimes elaborate forts.
The main characters in the Angry Birds game story are the angry birds themselves and the green pigs. The angry birds include the red bird which is kind of the basic and common one, and then there are other birds with special abilities like the yellow, blue, black birds etc. The green pigs are the antagonists who stole the birds' eggs.