A different plot could be that Harry is targeted by a powerful curse that gradually drains his life force. As he nears death, he tries to pass on his knowledge and skills to his friends, especially his knowledge of the dark arts and how to combat them. His death then serves as a catalyst for his friends to become stronger and more united in their fight against evil.
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.
Perhaps in the fanfic, Harry dies in a freak accident during a Quidditch match. His broom could malfunction and send him crashing to the ground. This would cause a great outpouring of grief among the wizarding community, especially his friends at Hogwarts. His death would also leave a void in the fight against any potential dark threats as he was seen as a symbol of hope.
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.
One possible plotline could be that it explores the emotional aftermath for Sakura. Maybe she has to deal with feelings of loneliness and guilt, even if she wasn't directly responsible for their deaths. It could also show how she rebuilds her life without her family's support.
One possible plotline could be that Luna sacrifices herself to save Equestria from a powerful and ancient evil. She might use all of her magic and strength to defeat the foe, but in the process, it drains her life force completely.
One possible plotline could be Hermione trying to find a way to bring Crookshanks back. She might search through ancient magic books in the Hogwarts library, desperate for a solution. Another could be her reflecting on all the memories she had with Crookshanks, like when it helped her and Harry figure out things. She could also become withdrawn from her friends for a while as she mourns, and they would have to find a way to reach out to her.
A plotline could involve Konata's death being a mystery. The other characters might try to figure out what happened to her. They could discover some secrets she had been keeping that might be related to her untimely death. Maybe there was something she was involved in that she didn't tell anyone about, and her friends piece it together as they investigate.
One possible plotline could be that Tomoya sacrifices himself to save Nagisa from a terminal illness. In the original story, he's very dedicated to her, so in a fanfic, he might give his life force or something similar to ensure her survival. This would leave a huge impact on the other characters, especially Ushio, who would grow up without her father.
In this fanfic, it could be that Deku's quirk goes out of control during a training exercise. He loses the ability to contain his power and it ends up consuming him, resulting in his death. This would create a lot of self - reflection among the other students about the risks of their quirks and the importance of proper training and control.
Perhaps in the fanfic, Bakugo dies due to a tragic accident. For example, he could be involved in a training exercise that goes horribly wrong. His death would then shock the entire U.A. High School. His classmates would struggle to come to terms with it, and it might cause some of them to question the safety measures in place at the school. It could also be a turning point for the story, leading other characters to be more cautious and less reckless in their actions.
One possible plotline could be that Naruto is on a highly dangerous mission alone, perhaps against an extremely powerful and unexpected enemy. He might sacrifice himself to protect his village or his comrades. For example, he could be facing a new type of jinchuriki whose power he underestimated, and in the end, he uses all his strength to seal the enemy away, but at the cost of his own life.