It could be Sasuke. Maybe Sasuke is in a bad mood on Naruto's birthday and rejects Naruto's invitation to hang out or something. Since they have a complex relationship, Sasuke's rejection would really hit Naruto hard.
In this kind of fanfiction, Naruto might feel extremely sad and lonely on his birthday. Maybe his friends forget his birthday, or he is rejected from a special event or by someone he cares about. It could lead to him reflecting on his relationships and his place in the village.
In the fanfiction, it might be that Naruto had different ideals and goals from his family. His strong will to pursue his own path of becoming Hokage, for example, could clash with the family's expectations, causing him to reject them.
Common themes in this type of fanfiction include betrayal. Naruto feels betrayed by his family, which colors his view of the world. Redemption can also be a theme, either Naruto seeking redemption from his family or his family later seeking redemption from him. And the theme of growth in solitude. Naruto grows and becomes stronger while being alone, without the support of his family.
This is a really dark concept. In fanfiction, such a scenario might be written to explore extreme emotional distress. Maybe the author wants to show how much pressure Naruto has endured secretly, and on his birthday, which is supposed to be a happy day, it all becomes too much to bear. However, in the original Naruto story, Naruto is a character full of hope and perseverance, so this is a very different take.
It might change the relationships of other characters. For example, his friends might be caught in the middle, trying to understand Naruto's decision and also deal with the family's reaction. This could create a complex web of emotions and storylines in the fanfiction world.
He might meet an old sage who has been living in seclusion near the village. The sage could see Naruto's loneliness on his birthday and offer him some ancient ninja knowledge.
Well, in such a fanfiction, it usually makes Naruto's journey even more tragic. It can lead to him becoming more independent and relying only on himself. He might develop a stronger sense of self - discovery as he has no family support. This can also result in him having different relationships with his friends. For example, he may be more hesitant to trust them at first, but as they prove their loyalty, those friendships become even more precious.
In this fanfiction, Naruto could be visited by the spirit of his father, Minato. Minato could offer some words of wisdom and comfort to Naruto on his birthday. They might have a heart - to - heart conversation about Naruto's growth as a ninja and his future in the village.
To make it stand out, focus on the emotions. Show Naruto's genuine surprise and joy at the celebration. You can also include some rare characters in the celebration, like the old Hokages coming back as spirits to wish him well.