Snape's death was to show that you could always choose to change your path. From a seemingly villainous character, he was finally revealed to be kind. He had been secretly protecting Harry and following Dumbledore's orders to infiltrate the Death Eaters. His death had a profound meaning in the whole story. Harry Potter and the Order of the Phoenix is not enough. Please click to read the novel!
In the original novel, Voldemort did not slit Snape's neck with his wand. Instead, he had Nagini attack Snape, and he did not resist, allowing Nagini to bite his body. Voldemort had his reasons for doing so. After all, he had thought that Snape was the owner of the Elder Wand, and that attacking Snape with Avada might backfire. He believed that Nagini's venom was enough to kill Snape, so he took Nagini with him and left the Shrieking Shack. Harry, who had been watching from the sidelines, was still breathing when Harry approached Snape, and it was at this time that Snape handed his last "gift" to Harry, his tears. The Dark Lord's voice echoed throughout Hogwarts, which caught Harry's attention and caused him to return to school without confirming Snape's death. Harry Potter and the Order of the Phoenix is not enough. Please click to read the novel!
In the movie, Voldemort was worried about the rebound of the spell (because he believed that Snape was the master of the Elder Wand and that the Elder Wand would not harm its master, and he had experienced the rebound of the spell before). Instead of using the spell, he used the Elder Wand as a dagger to cut Snape's neck, and then called Nagini to bite Snape to death. In the original novel, Voldemort was afraid of Snape's strength. Even if he did not consider the Elder Wand, he might not be able to kill him in a one-on-one PK. So Voldemort and Nagini cooperated. Voldemort waved his wand to distract Snape, Nagini covered Snape with a magical cage, and Nagini's fangs sank into Snape's neck, killing him. Harry Potter and the Order of the Phoenix is not enough. Please click to read the novel!
Perhaps an old enemy from Snape's past, someone who has a long - standing grudge against him. This person could have tracked him down to the Shrieking Shack and finally got their revenge. It could be someone related to his days as a Death Eater or even from his school days when he might have made some enemies.
In Snape's death fanfiction, one common emotional reaction is shock. Readers are often stunned by his sudden death, just as it was in the original story. Another is sadness. Many fans feel a deep sense of grief because Snape was a complex and ultimately heroic character. There's also a sense of admiration that might be explored in fanfiction. His selfless act of protecting Harry Potter until the very end makes him a figure worthy of admiration, and fanfiction might delve deeper into how other characters come to fully realize his true nature and sacrifice.
Harry Potter might react with a newfound understanding. In the original story, he named his son after Snape. In fanfiction, this could be explored more deeply. He might feel guilty for not seeing Snape's true intentions sooner. Hermione could react with her typical intelligence - led analysis. She might try to piece together Snape's actions over the years and come to a more complete understanding of his character. Ron, on the other hand, might be more straightforward in his grief. He might be sad that someone who was on their side all along had to die in such a way.
There are several. Some focus on Snape's early days as a Death Eater. For example, in one fanfic, it details how he was recruited, his initial thoughts on Voldemort's ideology, and how he gradually started to question it. It also shows how his relationships with his fellow Death Eaters were formed and evolved over time.
There's also the possibility that it was an accident. Fanfiction often plays with the idea of magical accidents. Maybe a spell misfired during a demonstration or a fight that broke out among the Death Eaters that Snape got caught in the middle of, and as a result, he got injured.
One common theme is Snape's internal conflict. Since he was a double agent, fanfictions often explore the turmoil he felt between his loyalty to Voldemort as a Death Eater and his real allegiance to Dumbledore. Another theme is his relationships with other Death Eaters, like Bellatrix or Lucius.
Snape could be very cautious in his interactions. He would be constantly aware of the power dynamics. He might flatter the more powerful Death Eaters subtly to avoid suspicion. For instance, he could compliment Bellatrix on her loyalty to the Dark Lord. At the same time, he might try to intimidate the weaker ones to show that he's not to be trifled with. He might use his knowledge of the Dark Arts to his advantage in these interactions, like casually mentioning a difficult spell he's mastered to gain some respect.