The fans themselves could be main characters. They could be shown dealing with their emotions, sharing memories of the singer, and trying to keep the singer's legacy alive. For example, a group of super - fans might form a club dedicated to the singer after the death.
Perhaps in the fanfic, the singer's death is a mystery, and fans start to investigate, uncovering secrets about the singer's life that were previously unknown. This could involve looking into the singer's relationships, unfulfilled dreams, or hidden talents.
The main character could be an ordinary citizen who just happens to be in the wrong place at the wrong time and gets kidnapped. For example, a tourist visiting America.
Obviously, Catherine Rollins herself could be a central figure even though she dies. Her memory could play a big role in the story.
A politician who drives the empire - building policies could be a main character.
There could be a young and ambitious trainer named Alex. He's on a quest to become the best Pokemon trainer in America.
A rogue ninja from another village could be the main antagonist. Maybe a ninja from the Hidden Mist Village who has a personal grudge against Konoha and sees Naruto as the symbol of Konoha's strength. So, he devises a complex plan to take down Naruto. This ninja could have some unique and deadly jutsu that Naruto has never faced before, which ultimately leads to his downfall.
It could be a powerful sorcerer who wants to take over Crookshnks' homeland. This sorcerer has dark magic and sees Crookshnks as a threat to his plans, so he devises a scheme to eliminate him.
Since I don't know the specific fanfic, Sakura is likely one of the main characters as it's in the title. There may also be characters related to her, like her friends or family who are affected by her death in the wave.
Obviously, America would be the main character. There could also be some sort of selection committee or judges as supporting characters.
The singer might be a struggling indie singer trying to make it big. The girl could be a waitress at a local bar where the singer often performs. She encourages him with her kind words and they end up falling in love.