In most proper Harry Potter fanfiction, McGonagall is a strict but fair character. If Harry were to break school rules in a fanfic, she might punish him as she does in the original books. However, it depends on the plot and the writer's interpretation of her character.
There's also 'McGonagall's Legacy'. This fanfiction focuses on how McGonagall influenced generations of students. It has some really heart - warming moments as it shows her teaching and mentoring. It gives a new perspective on her character that you might not get from the original books.
Some characters in the harem might be developed as admirers of McGonagall's strict yet fair teaching style. They could be shown as constantly trying to impress her with their magical skills, like a young wizard who practices transfiguration just to get her attention.
I'm not sure if there is a specific fanfic with that exact plot. Fanfiction can cover a wide range of ideas, but this one seems quite unusual. Most fanfics tend to focus on more traditional themes like Harry's adventures at Hogwarts, his relationships with his friends, or the fight against Voldemort. However, in the huge realm of fan - created content, it's possible that something like this exists, but it's not likely to be very popular.
He could teach a class on Ancient Runes. There are so many mysteries surrounding the runes in the Harry Potter world, and he could be an expert in deciphering them. Maybe he's even discovered some new uses for the runes that could be useful in modern - day wizarding society. Another option is a class on Magical Histories of Other Continents. Since the main focus in the books is on the UK wizarding world, his class could explore the magic of places like Africa or Asia.
Well, in this fanfiction, Harry might be a professor because of his extensive knowledge and experience in magic. He could be teaching younger students and sharing his wisdom.
One great fanfiction could be 'A Bond Beyond Hogwarts'. It explores the unique relationship between Harry and Minerva in a post - war Hogwarts setting, with Harry seeking Minerva's guidance on becoming a better wizard and leader.
Another theme is wisdom. Since McGonagall is a very wise character, many fanfictions explore how she imparts her wisdom to others, especially Harry. They might have her giving advice on dealing with Voldemort or handling the pressures of being a young wizard in a dangerous time.
Her connection to the Gryffindor house is also a common theme. Some fanfics focus on her pride in the Gryffindor students and how she upholds the values of the house. She could be shown guiding Gryffindors through tough challenges and helping them grow into true Gryffindors.