Think about the themes in Fairy Tail that can be turned into a sad story for your OC. For instance, the concept of friendship. Your OC could be betrayed by a supposed friend in the guild. Develop the OC's character arc in a way that shows their downward spiral into sadness. Show their reactions, like crying alone in their room or avoiding the guild members they used to be close to.
One sad OC (Original Character) fanfic in Fairy Tail could be about an OC who loses their magic abilities. This would be a really tragic story as in the Fairy Tail world, magic is such an important part of one's identity. The character would have to struggle with feelings of worthlessness and isolation.
One sad Nalu story could be about a time when Lucy is in great danger and Natsu is too far away to reach her immediately. He races towards her, fearing the worst, and the sense of impending loss makes it a sad moment. For example, when Lucy is captured by a powerful dark guild and Natsu is on a different mission. He feels helpless and full of self - blame.
There are fanfictions that blend the music of Fairy Tail with different art forms within the story. Say, a fanfic where the guild members put on a musical performance using their magic in a really unique way. It could also be about a mysterious musician who joins the guild and brings a whole new musical dimension to their adventures, changing the dynamic of the group.
The character development. If a fanfiction shows a character's downward spiral in a believable way, it becomes sad. For example, if Happy suddenly loses his ability to fly in a story. His normally cheerful self would be so devastated, and seeing his friends try to cheer him up but fail would be really sad.
A sad Fairy Tail fanfiction could focus on Erza. Maybe she gets trapped in a magical dimension where she is all alone. She has to relive all her worst memories and fears. The guild tries their best to get her back, but she starts to lose her will to fight and the fanfiction could explore her inner turmoil and the sadness of being isolated.
It can be a powerful emotional trigger. When a character plays music from the heart, it can convey their true feelings to other characters. For example, if a character is in love but can't find the words to say it, a heartfelt song might express those emotions better.
Well, music in Fairy Tail fanfiction can add a lot of depth. It can set the mood, like if it's a sad song, it might be used during a character's moment of loss or sacrifice. For example, if a beloved character dies, a slow, melancholic tune in the story can make the readers feel the pain more acutely.
Another interesting plot could be a young wizard who is initially not good at traditional magic but has a natural talent for music magic. They struggle to be accepted in the Fairy Tail guild at first because their magic is so different. However, as they grow and develop their skills, they end up saving the guild from a powerful enemy using their music magic in a very unexpected way.
First, you need to be familiar with the Fairy Tail world, including its characters, magic system, and overall atmosphere. Then, think about how music can be integrated. It could be as simple as a character being a talented musician. Next, create a plot that revolves around the music. For example, a music competition in the Fairy Tail world.