Well, first to get him to be hostile, you need to gain access into his room on the top floor of the Circle of Trust Inn (the Inn is located directly opposite the talking tree/entrance to Crow's Nest).
To do so, you have to get the Anti-Demon Grip scroll from the Forbidden Archives in the Prancing Seahorse.
Use the scroll on the door and voila, he'll appear once you are trying to leave the room.
Tackle him and beat him with his own legs. Figuratively.
