Shard's Links
Whilst Acheron may act as though they hate their mortal father when around their siblings or other hellhounds, Acheron actually frequents the mortal realm specifically to visit him in secret. They implore to try and better their relationship with their father, despite how rocky things may have been between them in the past.
Fenrir is frankly honored to have some semblance of his relationship with his pup, and although the initial meetup was a great shock to both of them, he hopes to be able to patch things up and be a good parental figure to Archeron.