One possible theme could be sacrifice. Maybe Twilight Sparkle sacrifices herself to save her friends or Equestria. Another theme might be dealing with grief among the other ponies after her death.
I really don't think it's a good idea to focus on 'twilight sparkle death fanfic'. The 'My Little Pony' franchise is mainly about friendship, magic, and positive values. Reading such dark fanfics might not give you the best experience. Instead, you could look for fanfics that show Twilight Sparkle's journey in learning new spells or making new friends in Equestria.
Twilight Sparkle is a beloved character, so a death fanfiction would likely be quite controversial. However, it could also be a creative way to re - imagine the story. For example, her death could lead to a new villain emerging or a different power structure within the Equestria setting. It all depends on the author's intentions and how they choose to handle such a significant event.
One aspect that makes it unique is the emotional impact. Twilight is a central character, so her death would shake up the whole story. It's different from minor character deaths.
Twilight would be devastated. She might go into a state of shock at first. Then she could become very withdrawn, shutting herself away in her library to grieve. Eventually, she would probably turn her grief into a determination to uphold her brother's values and use her magic to protect Equestria even more vigilantly.
One common theme could be sacrifice. Maybe in the fanfic, Twilight Sparkle sacrifices herself to save her friends or Equestria. Another theme might be the reaction of the other characters. Her friends could go through a period of intense grief and then find a way to carry on her legacy. For example, they might strive to complete a task she started.
The appropriateness of a 'twilight sparkle diaper fanfic' is highly subjective. Some people might find it completely inappropriate due to the rather strange and unorthodox combination of the character and the diaper concept. Others, if the story is written in a very innocent, perhaps even child - like way, might see it as just a creative and quirky piece of fanfiction. But overall, it's not a type of fanfic that would be considered appropriate for a wide - ranging and diverse audience.
An 'evil twilight sparkle fanfic' is simply a fan - made fictional story where Twilight Sparkle is portrayed as an evil character. Fanfic writers might do this to add a new and unexpected twist to the familiar My Little Pony story. It could be inspired by things like exploring what would happen if Twilight's thirst for knowledge turned into a more self - serving and malevolent pursuit, or if she was corrupted by some dark magic.
In some fanfictions, she could die sacrificing herself for her friends. Twilight is extremely loyal to her friends in Ponyville. So, if there was a situation where her friends' lives were in danger, like from a powerful villain, she might choose to give up her own life to protect them. This would be a very heroic and in - character way for her to die.
I'm not entirely sure specifically as it could refer to many different fan - created stories about Twilight Sparkle that have been forgotten. It might be a fanfic that was once popular but has since faded from the spotlight, perhaps due to new trends in the fandom or simply being lost among the vast number of fanfics out there.