One possible storyline could be that in a battle against a powerful dark wizard, Harry sacrifices himself to save Hermione from a fatal curse. Another could be that he gives up his life to protect Hermione from a dangerous magical artifact that is about to explode. Or perhaps he takes on a deadly disease that was meant for Hermione, knowing it would cost him his life.
In some versions of this fanfiction, Harry might die for Hermione in a more political or strategic sense. Let's say that there is a group of dark wizards who are after Hermione because of her knowledge and potential power. They plan to use her to achieve their evil goals. Harry, aware of this, pretends to be Hermione and lures the dark wizards away. In the ensuing battle, he is outnumbered and overpowered, but he manages to hold them off long enough for Hermione to be hidden safely. Eventually, he succumbs to his injuries and dies, knowing that Hermione is alive and can continue to use her skills to fight against the forces of darkness.
Perhaps Ginny discovers some hidden secrets or powers within herself as she copes with Harry's death and the pregnancy. Maybe she has to deal with people who question her ability to raise the child without Harry. The story could also focus on how the child grows up with the legacy of Harry, and whether the child inherits any of Harry's special abilities or traits.
One possible storyline could be that Voldemort manages to attack the Dursleys' house before Hagrid can arrive to take Harry to Hogwarts. Maybe a Death Eater discovers Harry's location early on and Voldemort decides to end the threat immediately. Another could be that some dark magic from Harry's parents' past catches up to him as a baby, and he succumbs to it, never making it to Hogwarts. It could also be that a wizarding accident occurs in the Muggle world that involves Harry and results in his death, like a misfired spell from a rogue wizard in hiding.
One possible plot development could be that Hermione is left with a deep sense of guilt and responsibility. She might then take on Harry's mission or cause in his memory. For example, if they were fighting against a new dark wizard, Hermione could become even more determined to defeat the enemy.
Another idea is that Hermione gets influenced by a dark magic book that she thought was just a regular old magic theory book. The book slowly plants ideas in her head that Harry's power is too dangerous and must be curbed. As a result, she might start to use hexes on Harry in a misguided attempt to keep the peace at Hogwarts.
One possible storyline could be that Ron sacrifices himself to save Harry during a final battle against Voldemort. His death could be a turning point for Harry, making him more determined to defeat the Dark Lord. Another idea is that Ron is poisoned by a new dark magic spell created by Death Eaters, and his death causes Hermione to go on a vengeful quest against the Dark Arts. Maybe in a different take, Ron dies trying to protect his family from a group of rogue werewolves, and his death shatters the Weasley family but also unites them in a fight for justice.
One possible storyline could be that their daughter inherits both Harry's courage and Hermione's intelligence. She might face a new threat at Hogwarts that combines elements of old dark magic and new, unknown forces. Maybe she discovers a hidden chamber that holds secrets about their family's past, leading to an adventure filled with mystery and danger.
One possible storyline could be that as Peter Pan dies, Tinker Bell uses all her magic in a desperate attempt to save him. She might make a deal with the Neverland's dark forces, sacrificing her own well - being for his life.
Perhaps in this fanfiction, Naruto is fatally injured in a fight during the Chunin Exams. He might sacrifice himself to save one of his friends. This would cause a great outpouring of grief from his friends and mentors. The village would also be in shock, and there could be a change in the power dynamics as his absence leaves a void.
A common scenario in such fanfictions is that Hinata sacrifices herself in a war - torn situation. For instance, in a great ninja war, Naruto is the key to victory but is targeted by the enemy's most powerful forces. Hinata, with her unwavering love for Naruto, jumps in front of a massive attack aimed at Naruto, knowing full well that it will cost her life. This selfless act then serves as a major turning point in the story, inspiring Naruto and his comrades to fight even harder.
One possible storyline could be that Naruto is framed for a serious crime within the Blood Prison. The corrupt prison system then subjects him to various forms of torture and unfair treatment, which eventually lead to his death. Maybe he was protecting someone else inside the prison and took the fall for a crime he didn't commit.