Well, Naruto could initially be shocked that no one remembers. But then he might try to play it cool, because that's his nature. He could also think that they might be planning a surprise later. However, as time passes and still no one remembers, he would start to feel really down. He might even go off on his own to brood about it, wondering if he's not as important to his friends as he thought.
There's a chance it could be Shikamaru. Despite his laid - back attitude, he is quite perceptive. He might notice Naruto's subdued mood and put two and two together, realizing it's his birthday. Then he could rally the others to quickly put together a belated celebration for Naruto.
Well, the plot could be about Percy feeling really sad and left out when everyone forgets his birthday. Maybe he starts to question his friendships. He could go off on his own for a while, and then his friends realize their mistake and try to make it up to him with a big, surprise celebration.
Well, obviously Merlin is one of the main characters since it's his birthday that's being forgotten. Arthur is often another main character. He might be one of those who forgets, or he could play a role in trying to make up for the forgetfulness later. Gwen could also be a main character, perhaps being too busy with her own tasks to remember Merlin's birthday.
It could. In many fanfictions where everyone forgets Merlin's birthday, it might end sadly as Merlin feels isolated and unloved. He might have expected at least one person to remember, and when no one does, it could lead to a melancholic conclusion with him feeling deeply disappointed and alone.
Obviously, Percy would be the main character. His friends like Annabeth, Grover, and the others from his group would also be important characters. They are the ones who forget his birthday, so they play a big part in the story as they deal with the consequences of their forgetfulness.
In such a fanfiction, Naruto might find himself in a very lonely and confusing situation. He would have to relearn about his relationships and the world around him. Maybe he'd be more cautious as he doesn't remember who is friend or foe.
Reddit can also be a good place. There are Naruto - related subreddits where fans sometimes share or discuss interesting fanfics. You could post a request for 'everyone forgets naruto fanfic' and see if anyone can point you in the right direction.
One good 'everyone forgets naruto fanfic' could be those that focus on minor characters' backstories. For example, a fanfic about the life of a Chunin who was overlooked in the original series. It gives depth to the Naruto universe in a different way.
One way the plot could develop is that Naruto begins to trust the wrong people because he doesn't remember who he should trust. This could lead to him getting into dangerous situations. Meanwhile, his true friends are desperately searching for a way to reverse his memory loss. As the story progresses, Naruto might start to have flashes of his old memories, which would add some mystery and hope to the plot.