Well, if Harry obliviates everyone, it's a huge deal. Imagine all the memories gone! Regarding hiding fanfiction, it could be that he wants to prevent some controversial or dangerous ideas in the fanfiction from influencing people. But obliviating everyone is not ethical. Maybe he could have found other ways to deal with the fanfiction situation, like talking to the authors or setting some rules.
In some fanfics, if Dumbledore obliviates Harry, it could lead to a very different story. Harry might lose his memories of Voldemort, his friends, and his magical adventures. This could cause chaos as he tries to figure out who he is without his past knowledge. It could also lead to new relationships and character developments as he starts from scratch, perhaps even changing the course of the wizarding world's battle against the Dark Arts.
I'm not entirely sure specifically what that particular 'harry hides abuse fanfiction' is about without reading it. But generally, it might be a fan - created story where the character Harry is somehow involved in hiding abuse. It could be related to abuse within a magical world context, like hiding the abuse of magic by certain characters or perhaps hiding the abuse of other students at Hogwarts if it's related to Harry Potter fanfiction.
Perhaps he is trying to hide his true self. He may have a side of him that he doesn't want others to discover, like some special abilities or a different origin. So, being cold to everyone helps him keep his secrets and avoid getting too close to people who might figure him out.
You could start by looking on popular fanfiction websites such as Archive of Our Own (AO3). It has a vast collection of fanfictions from various fandoms, and there's a good chance you might find 'harry hides abuse fanfiction' there if it exists. Another option is Fanfiction.net, which is also a well - known platform for fan - created stories.
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.
Obviously, Harry Potter is the main character as it's about him hiding his power. His friends, like Hermione Granger and Ron Weasley, are also likely to be main characters. They might be in the dark about his hidden power at first, which could create some interesting dynamics in their relationships.
His closest friends like Ron and Hermione would probably be the most affected. They are used to having Harry around and relying on him. His sudden ignoring would leave them confused and worried.
One reason could be a misinformation campaign. Some malicious wizard or witch might have spread false rumors about Harry, making everyone believe that he has done something terrible like being in league with Voldemort again.
Harry could enlist the help of some of his most trusted friends like Neville and Ginny. Neville could use his knowledge of Herbology to create magical plants that act as sentinels around the hiding place. Ginny, with her powerful magic, could help set up wards. Together, they form a sort of protective circle around Hermione and Luna. Also, Harry might use his Invisibility Cloak to move around undetected when getting supplies for them.