The sword could be a magical artifact she discovers during one of her adventures in the Everfree Forest. Maybe it was left there by an ancient unicorn or alicorn for a worthy magic user to find.
She might use it to deflect dark spells. The sword could have the ability to absorb or redirect magic, so Twilight can use it to send enemy spells back at them.
A really popular one is the fanfiction that focuses on Twilight's relationship with her friends in the Equestria Girls setting. It shows how they support each other through school problems, boy - girl drama, and still manage to keep their magical bond intact.
There's also 'Sunset and Twilight's Adventure Beyond Equestria'. This fanfic takes them on a journey to a new land where they have to learn about a different kind of magic. It's full of exciting twists and turns as they face challenges together and grow as friends. It really delves deep into their characters and how they can rely on each other.
One great 'mlp twilight sparkle fanfic' is 'A Canterlot Wedding' fanfic. It delves deeper into the emotions and backstories of the characters involved in the wedding. Another good one could be 'Twilight's Ascension' which explores Twilight's growth in magic in unique ways.
One possible plot could be that Twilight Sparkle gets turned into a zombie pony through some dark magic or a strange virus in Equestria. Her friends then have to figure out how to either cure her or deal with her new zombie state while still maintaining their friendship.
A fanfiction could involve Dusk Shine and Twilight Sparkle exploring an ancient, forgotten library in Equestria. They stumble upon a book that holds the secrets to a long - lost magic. As they study the book, they face challenges from other ponies who want the power for themselves. Their friendship would be tested as they protect the knowledge and each other.
In the fanfiction, their characters could develop in relation to each other. For example, Twilight Sparkle's studious nature could rub off on Flash Sentry, making him more interested in learning. On the other hand, Flash Sentry's adventurous spirit could encourage Twilight to take more risks and step out of her comfort zone. This mutual influence could lead to a more well - rounded development of both characters as the story progresses.