She might use her magic skills to shield Harry from physical harm. For example, she could cast protective spells like a strong shield charm when Harry is in danger from dark wizards. Also, she may use her authority in Hogwarts to keep him away from those who wish to harm him, like making sure he is not alone in dangerous areas of the school.
McGonagall could protect Harry by guiding him in his studies. By ensuring he has a good understanding of magic, he becomes more capable of protecting himself. In the fanfic, she might give him extra lessons or advice on how to deal with certain spells or magical creatures that could pose a threat to him. This way, she is protecting him in the long run.
Perhaps when Harry is wrongly accused of something, and McGonagall uses her influence and knowledge to prove his innocence. She stands up for him in front of the whole school or the wizarding authorities, which is a very significant moment of her protecting Harry.
Harry might be initially shocked and confused. He has always seen McGonagall as a reliable figure in his life at Hogwarts, so her abandonment would be a huge blow to him.
She might immediately comfort him. McGonagall is a strict but kind teacher. She could put a hand on his shoulder and say soothing words like 'There, there, Mr. Potter. It will be all right.'
She might react with her usual no - nonsense attitude. McGonagall is known for being strict but fair. So she would first listen carefully to Harry's problem, her eyes fixed on him, and then start to analyze the situation. She may not show much emotion on the surface, but deep down, she's concerned for Harry's well - being.
It could be that in the fanfic's plot, McGonagall has some past connection to Harry's enemies. So, her hatred towards Harry is a result of her loyalty to those she has a history with. This would create a lot of drama and conflict within the fanfic's story.
McGonagall might be initially shocked. She's a strict teacher and not used to such an informal and deeply emotional form of address. But then she could feel a sense of warmth and responsibility towards Harry. She might start to show more care in her actions, like making sure he eats well in the Great Hall or checking on his studies more closely.
One possible reason could be that she is under some sort of dark magic influence. Maybe a spell has been cast on her that makes her act out of character and abandon Harry.
McGonagall often serves as a mother - like figure in fanfiction. She might comfort Harry when he's facing difficulties with Voldemort or other challenges at Hogwarts. Her influence is seen in how Harry approaches problems. He learns from her to think calmly and use his wits, rather than just relying on his Gryffindor bravado. This helps him make better decisions and grow into a more well - rounded wizard.
She might be initially cautious. Given that becoming an Animagus is a complex and dangerous process, she would likely want to ensure Harry fully understands the implications. She could start by asking him why he wants to become one.
McGonagall might notice Harry's distrust and feel hurt or frustrated. She may try to figure out what went wrong but find it difficult as Harry is not forthcoming. Their interactions become less warm and more formal. For example, in class, Harry may be less likely to ask for help from McGonagall, and McGonagall may be more strict with Harry as she doesn't understand his change in attitude.