Harry Potter FanFiction:

Hannah Longbottom liked to watch the people who entered the Wizarding World via the small, walled courtyard behind the Leaky Cauldron for a reason: During her not so long life, she had learned about three different boys who had entered the Wizarding World alone, leaving behind a life so horrible she could barely imagine. One of them, who became a friend of hers, had gone through great hardships to become a hero, one of the greatest wizards the Wizarding World had ever seen. One of them, who had been her teacher, had become cold and bitter, and no one had ever recognized what amazing talents he could have offered, until it had been too late. One of them, the monster she had helped to fight during the Battle of Hogwarts, had become the most dreaded, most dangerous, and most deadly man Great Britain had ever seen, and yet it could have all been different, if someone had just tried to make that difference early enough in that life, if he had not boarded the train to Hogwarts all alone.

Already posted at Devianart and AO3, I've included a link to RoyalRoad on my profiles there.