I got this achievement by Completing the quest “ Ill Met By Moonlight.”
I believe it starts in the town of Falkreath, if this is wrong correct me because I forgot, but in this town there should be a graveyard with some tombstones and a few people walking around. There will be a priest there, an elf priest, giving the funeral for a 10 year old girl. The two other people by the priest are the girl’s mother and father.
I spoke to the father and asked him every question, he tells you about a man named Sinding who killed his daughter
The quest will update and Sinding is located in the same town in a jail, the arrow will relocate as you progress through this quest and point you in the right direction to find the building he is in.
Find Sinding and talk to him, say you will take the ring from him and give it to Hircine, who is a Daedric Lord. The quest will send you to kill a Giant White Stag, I suggest being a decent level and sneaking up on this stag so it doesn’t run away forever like it did to me. Use a bow and sneak or stealthily walk up to it and attack.
Once the stag is dead, its ghost will appear and it will be Hircine, talk to him and ask if he can remove the curse from the ring, he will send you to find and kill Sinding in Bloated Man’s Grotto. Once there, there should be a few hunters that have been killed, continue on and Find Sinding in Werewolf form and tell him that you will spare his life, help him kill the remaining hunters and in doing so you become his friend and upon exiting the cave, Hircine will be pleased by you telling him that you were unable to kill Sinding. Hircine will still be pleased because, instead you slaughtered all the hunters and impressed him, after a very short dialogue you will receive his blessing and the achievement is yours.
Sorry for the long guide, just giving you’re the full step by step instructions