He might turn to his studies more intensively. Since he has no friends to distract him, he could pour all his energy into learning new spells and magic, becoming more powerful in the process.
One interesting aspect could be the unique plot ideas that were left unfinished. For example, some might have had really creative takes on the wizarding world's history or new magical creatures. Another aspect is the different character developments that were being explored. Maybe a fanfiction was showing a side of a character we don't see much in the original series. Also, the writing styles in these abandoned works can be fascinating as they often vary from very formal to extremely creative and unorthodox.
One way is to search on some old - school fanfiction websites. There are often archives where you can look for works that haven't been updated in a long time. Another option is to ask in Harry Potter fan communities. There are people there who might know of some abandoned works or have a collection themselves. You can also try searching for specific keywords like 'abandoned' along with 'Harry Potter fanfiction' on search engines, but this might be a bit hit - or - miss.
Some potential new allies could be the house - elves. They might see Harry's plight and decide to help him, using their unique magic and knowledge of Hogwarts' secrets. Another could be the centaurs in the Forbidden Forest. They are very wise and may take Harry under their wing.
She could face a lot of challenges. For one, the language barrier would be difficult. She'd have to learn Japanese to communicate and study in the new magical environment. Also, the Japanese magical society might have different views on her status as an outsider, and she might have to prove herself worthy to be part of their community. However, she is Harry Potter after all, so she would likely adapt and grow in this new setting.
One reason could be that the author lost interest. Maybe they started with a great idea of a female Harry Potter but then got distracted by other things in life or new fanfiction ideas. Another reason might be that they received negative feedback which demotivated them from continuing.
One way to find fem Harry Potter abandoned fanfiction is to search on fanfiction - specific platforms like Archive of Our Own. Use the search terms 'female Harry Potter' and 'abandoned' to narrow down the results. There might be some really interesting stories that didn't get completed but still have great concepts.
There could be an American wizard who takes Harry under his wing, like a gruff but kind old wizard named Alistair. He could teach Harry about American magic in a no - nonsense way.
One possible plotline could be Harry growing up in an American wizarding community that has different traditions and values compared to the British one. He might have to adapt to new spells and magical practices.
One possible storyline could be that Harry discovers his friends have been influenced by dark magic or a powerful spell that makes them shun him. He then has to find a way to break the spell while also dealing with his own feelings of betrayal and isolation.