Will is a nine-tailed-fox helplessly in love and Hannibal is an oblivious cannibal.
The fox lunges at him.
His hand shoots out and grasps it by it's neck. It would be so easy for him to snap it's neck, just a quick tightening of his fingers-
He releases the fox. "I'm letting you go, little fox," he says, using its state of disorientation to quickly grasp the trap by the jaws.
In which Harry is raised by Dr. Hannibal Lecter and released into the wizarding world. Nobody is ready.