Another idea is that there is a powerful dark wizard other than Voldemort at Hogwarts. This wizard has been hiding in plain sight all along. In Harry's fourth year, he decides to make his move. He uses a powerful dark spell during one of the Triwizard events. Harry, being in the wrong place at the wrong time, is directly affected by the spell and dies instantly, without anyone really knowing who was behind it at first.
One possible plotline could be that Harry Potter sacrifices himself to defeat an even more powerful dark wizard than Voldemort. Maybe this new enemy has a power that can only be countered by Harry's self - sacrifice, which would lead to a very bittersweet ending for the wizarding world.
A plotline could be that Ron is killed in a magical accident during an experiment gone wrong. This accident might be related to some new, dangerous magic that he was trying to master. His death would shatter the trio. Harry would feel guilty because he might have been involved in the experiment in some way. Hermione would be grief - stricken and would pour herself into research to try and understand what went wrong. The fanfic could then explore how the wizarding community reacts to Ron's death, with some blaming Harry and Hermione, and others mourning the loss of a great wizard. It could also show how Harry and Hermione have to grow and become stronger individually to face the challenges that come their way after Ron's death.
Voldemort would likely gain more power more quickly. With Harry out of the way, there is no one to oppose him directly in the prophecy sense. The Ministry of Magic would probably fall under his control even faster. The remaining resistance would be much weaker. Families would be afraid to send their children to Hogwarts. Enrollment might drop, and the whole wizarding education system could be in jeopardy. The magical creatures might also sense the shift in power and become more unruly as the balance in the wizarding world is disrupted.
One possibility could be that Voldemort manages to find and kill Harry much earlier. Maybe the protection spell that Lily cast fails due to some unforeseen dark magic interference. This would change the entire wizarding world. Hogwarts might be taken over by Death Eaters completely, and there would be no 'Boy Who Lived' to inspire hope. The Order of the Phoenix would likely be crushed much sooner, and the wizarding world would descend into a much darker and more oppressive state than in the original story.
One possible plotline could be that Voldemort realizes that Harry is the key to some greater power or knowledge that he wants to obtain. So, instead of killing Harry, he saves him from another dark wizard or a dangerous magical creature. Maybe he sees that Harry has a connection to an ancient magic that could help him rule the wizarding world in a more complete way.
One possible plotline could be Harry coming to power after a great war in the wizarding world. He then has to deal with rebuilding and unifying the different wizarding communities under his rule as emperor. He might face resistance from some traditional wizarding families who don't want to accept a new form of government.
In a 'Harry Potter is an assassin' fanfic, the plot could start with Harry being trained by an unknown and powerful wizard who has his own motives for creating an assassin out of Harry. This trainer could be someone from a far - off land or an ancient order. Harry then starts taking on targets within the wizarding world that are supposedly 'evil' but as he delves deeper, he realizes that things are not as black and white as he was told. His friends start to notice his strange behavior and he has to either come clean or keep lying to them. As the story progresses, Harry might have to make some tough choices between his loyalty to his friends and his new - found assassin duties, all while uncovering secrets about the wizarding world that were previously hidden.
One possible plotline could be that Harry sacrifices himself to defeat a new and powerful dark wizard. In this scenario, his friends are left to pick up the pieces and continue the fight against the remaining dark forces. Another plotline might involve Harry being poisoned by a mysterious and undetectable substance, leading to his slow and tragic death while his friends search desperately for a cure.
In the fanfic, Naruto could die from an unexpected illness. His parents, who have been watching over him in spirit, are devastated. They might try to find a way to communicate with the living to tell them how special Naruto was. The mourning process could involve them seeing how the village comes together to remember Naruto, with his friends and comrades sharing stories of their adventures together. This would make his parents realize the kind of person Naruto had become and how much he meant to everyone.
One possible reason could be that the events in the fourth year are extremely complex and dangerous. For example, the Triwizard Tournament has many life - threatening tasks. In a fanfic, the author might not want their character to compete because they want to avoid the high - risk situations. Another reason could be that the character in the fanfic has some personal issues or goals that conflict with participating in the tournament. Maybe they are more focused on uncovering a mystery within the school that has nothing to do with the Triwizard Tournament.