In general, the Twin Star Exorcist anime remains loyal to the manga. It manages to capture the key elements and the overall tone of the story. Some changes are made for better animation presentation and to control the pacing, but they are not substantial and don't stray far from the manga's core.
Overall, the Twin Star Exorcist show has some similarities to the manga, but there are also added or changed elements to make it more suitable for the screen. Some fans think it's a decent adaptation, while others have mixed feelings.
The uniqueness lies in the fact that it brings together two distinct fanbases. Fans of Naruto are used to the world of chakra and ninja clans, while fans of Twin Star Exorcist are familiar with the exorcist lore. In fanfiction, these two worlds collide. The unique powers, settings, and character archetypes from both series can be mashed up. For example, a story could have Sasuke using his Sharingan to detect Miasma, or Benio using her exorcist skills to fight against a Naruto - style rogue ninja. It's this unexpected mixing of elements that gives 'naruto x twin star exorcist fanfiction' its own special charm.
Yes, there are quite a few. You can start by looking on fanfiction platforms like Archive of Our Own. Some stories might combine the unique ninja world of Naruto with the exorcist themes of Twin Star Exorcist in really creative ways, like having Naruto characters learn exorcist techniques or Twin Star Exorcist characters visit the Hidden Leaf Village.
One popular theme is the crossover between the two universes. Fans like to imagine how the characters from Devil May Cry would interact with those from Twin Star Exorcist. Another common theme is character development. For example, exploring the backstories of the characters in more depth. Romance is also quite popular, whether it's between the main characters or some unexpected pairings.
The ending of Twin Star Exorcists manga is quite complex and involves a final confrontation between the main characters and the ultimate evil. It leaves some room for interpretation.