Through the Shattered Glass (слэш)

Five years after the war, Auror Harry Potter touches the Mirror of Erised and wakes up in James Potter's body on the Hogwarts Express—eleven years old, first year, 1971.
Sorted into Slytherin instead of Gryffindor, Harry becomes the unlikely protector of young Severus Snape. He doesn't bully. He doesn't follow house divisions. He sits at the Gryffindor table with his mother and refuses to leave Severus alone.
But changing the past is complicated. Older students notice. Lucius Malfoy notices. And as the years pass, Harry realizes the boy who shadows him everywhere—brilliant, loyal, defensive Severus—has become something more than a friend.