After Sirius refused to save him from the Dursleys, a desperate Harry will do anything to protect himself from their "tender treatment". He performs a dangerous ritual to enable him to become powerful enough to be free of the Dursleys and anyone who would try to mistreat him. It works, but with terrible consequences.

With the end of his third year, Harry has had enough. He has no intention of ever going back to the Dursleys, and he's had it with the entire world being out to get him. So, he takes matters into his own hands and performs a ritual. With far reaching, global consequences. Not a crossover!