It could be that a new character, someone from a far - off land that Naruto met during one of his travels, is involved in his secret life. This character could bring with them a different culture and set of skills that Naruto is learning from in secret, perhaps something that could revolutionize the way ninjas in the Hidden Leaf operate.
Well, obviously Hermione herself is the central character. But other characters could include her friends like Harry and Ron, who might be completely unaware of her secret life at first. There could also be new characters introduced, such as a mysterious mentor who is guiding Hermione in her secret magical activities. Maybe a powerful witch or wizard from a far - off land who has some connection to Hermione's family in the past.
It could be that Naruto is secretly training a new and powerful jutsu that he doesn't want anyone to know about yet. Maybe he's afraid that if his enemies find out, they'll try to stop him before he perfects it.
Obviously, Edward Cullen is often involved. In these fanfictions, he might be the first one to discover Bella's secret life, which could lead to some intense emotional moments between them. Another popular character is Jacob Black. His relationship with Bella could take on a new dimension if he finds out about her secret life.
It could be Hinata. In the original series, Hinata has a deep affection for Naruto. In a fanfiction, it would be a natural progression for her to be his secret fiance. Maybe they got engaged secretly to avoid some political unrest in the village.
It might also be Gaara. Their initial encounters were filled with tension, but as the story could be twisted in fanfiction, that could develop into a different kind of relationship. Gaara's own journey of self - discovery and Naruto's influence on him could be a basis for a romantic relationship in fanfic.
It could also be Kakashi. There might be fanfictions where he has some secrets related to Naruto. For instance, he might be aware of a secret mission related to Naruto that he has been keeping from everyone, which could be a major plot point in the fanfiction.
There could be a mysterious mentor figure who guides Naruto in his secret life. This person might have unique abilities and a deep understanding of the ninja world's secrets. Another potential new character could be a spy from another village who discovers Naruto's secret life and tries to use it to their advantage.
It could be an old sage or a hermit who has been watching Naruto from afar. They might decide that the time is right to reveal the secret to Naruto himself or to those around him for the greater good of the ninja world.
Edward is a likely candidate. Since he is so attuned to Bella, he might pick up on some strange behavior or scent that leads him to suspect she is hiding something.
Perhaps it's Draco Malfoy in a more complex and redeemed version of himself. He may have come to respect Hermione during their years at Hogwarts, and his secret admiration for her could be a way of showing his growth and change. He might secretly leave her gifts related to her love for books or magic, like a rare edition of a magical text.