Often, it could be a result of a specific magical event or encounter. For example, he might come across an ancient spell or a magical creature that somehow triggers the revelation of his animagus form. Maybe he's in a dangerous situation and his magic reacts in a way that reveals this new aspect of himself. This would add an element of excitement and unpredictability to the story. He could be facing a powerful dark wizard and in that moment of extreme stress, his animagus form emerges to save the day.
Another way in fanfictions is that he could be guided by a wise mentor. This mentor, perhaps an old and experienced wizard or witch, could see the potential in Harry for having an animagus form and guide him through the process. They might teach him special techniques and spells that help him to finally transform into his animagus form. This would also create a nice relationship dynamic within the story, where Harry has someone to look up to and learn from in this new aspect of his magical development.
In some fanfictions, Harry's animagus form could be a stag, similar to his father's Patronus. It would be a cool connection to his family heritage and his own magical abilities.
If Harry's animagus form is a large and powerful creature like a dragon, his familiar might be in awe of him. It could lead to a relationship where the familiar is very submissive and looks up to Harry for protection. For example, the familiar might be a little imp that hides behind Harry when they encounter other dangerous magical beings.
His Animagus form could be a black dog. Black dogs are often associated with mystery and protection in the wizarding world, and Snape, with his complex and often secretive nature, could fit this form. He's always lurking in the shadows, much like a dog might when it's guarding or observing.
If Harry lives in his animagus form in fanfic, his identity would be a big mystery. People around him would only see his animagus shape. This could lead to some really interesting scenarios. He could use this to his advantage when sneaking around Hogwarts. Also, his friends might have a hard time recognizing him at first. But as they get used to it, they could come up with special signals or ways to communicate with him while he's in his animagus form.
In this fanfiction, if Harry is Hermione's pet as an Animagus, he would likely use his animal instincts to protect her. For example, if there's a threat in the Forbidden Forest, his animal senses might pick it up before Hermione notices. He could also play a role in helping her with her research. Maybe he could lead her to some interesting magical creatures she's studying by leaving little hints in his animal form.
Another possibility is that he becomes a fox. Foxes are clever and sly, which are qualities that Harry has developed over the years. As a fox, he could use his wits to outsmart his opponents. He could also easily blend into the forest environment, which would be handy for hiding or sneaking around.
In many fanfictions, the choice of animagus form often reflects the character's personality. If female Harry is hiding in her animagus form, it could be a form that represents her need for freedom and escape. For example, a bird. A bird can fly away from trouble and see things from a different perspective, which might be important for her in a difficult situation. She could be using this form to gather information without being noticed.
Harry's life in his animagus form would bring a whole new perspective to his fight against Voldemort. He could use his animal abilities for stealth and speed. As an animagus, he could get closer to Voldemort's lair without being noticed. He could also use his form to lead Voldemort's minions astray. His presence as an animagus could be a symbol of hope for the wizarding world in a different way. Instead of the boy - who - lived, he could be the mysterious animagus that always thwarts Voldemort's plans.
Friendship is also a common theme. Harry's friends' reactions to his Animagus form can range from shock to admiration. And sometimes, his Animagus form can even strengthen his bonds with his friends. For instance, if he can use his form to rescue a friend in a tricky situation, it deepens their friendship.
One great 'Harry with Animagus form' fanfic is 'Harry's New Shape'. In this fic, Harry discovers he can transform into a majestic stag, much like his father's Patronus. It's really interesting to see how he uses this new ability in his adventures at Hogwarts and against the Dark forces.