I really like the fanfic 'Fairy Tail: The Lost Souls'. In this, the author explores what would happen if some of the main characters lost their magic abilities. It's interesting to see how they cope and find new ways to fight and protect their guild. It also has some really cool new character designs for the antagonists, which are inspired by the original art style of the 'Fairy Tail' anime and manga.
Overall, the Fairy Tail anime is a reasonably faithful adaptation. There are some differences here and there, but they don't significantly deviate from the manga's core elements. Some scenes might be expanded or shortened for the sake of animation pacing.
The Fairy Tail anime is known for its relatively close adaptation of the manga. It manages to capture the key elements and character developments. Although there are occasional additions or modifications, they usually don't stray far from the manga's essence.
The Fairy Tail anime ends around a certain point in the manga, but it's not a straightforward correspondence. There are some differences in the pacing and story arcs presented in the two mediums.