Excellent story! You really bring Fenrir to life; I love how you characterise him through his voice, and how his voice contrasts with that of Remus's father -- one truly believes Fenrir's anger at the likes of him. I also admire how you describe the pack dynamics, so plausible and keenly-observed, and never overdone.
Then there are great lines such as --“Of course not Remus,” his father assured him, but a part of him almost hoped that he would. -- Interesting how the coldness contrasts with Fenrir's hot fury. I'd be hard-pressed to say who is the crueler man. --We soon crested another hill, a higher hill, and we stopped and gazed at the moon that was our mother, and the boy pointed his nose at her and sang to her, as did I. And to our ears came the songs of our brothers and sisters as we gloried in the moon, in our strength, in the wolf! -- I'm quoting that entire bit because it's just so good. --and the young man had spirit. I killed him anyway, and scattered him through the wood. -- So painful. --“You’re mad! Life in prison as a reward! You are no wolf, Remus Lupin, but a wizard’s lapdog!” “And you are not?” he asked softly. -- Oh yes. As the Fenrirs of this world recognise all too rarely.