Eroos
DxD, Shinmai Maou, tsuki ga michibiku, or some fantasy type anime where they could act more freely, Tsuki ga michibiku would be great in that respect. And I have a question, if (I hope not) Fenrir has a child, will that child have the mother's species? Since there can only be one existence like Fenrir's at a time.
The Beginning After the End. Just make some changes to the story, Arthur and his family never suffered that attack by bandits and went to the city without a hitch, Fenrir could appear near that dragon's lair (I forgot her name, I haven't read it in a while), and saves the elf (I also forgot the name, LOL).
depends on the world's that you're considering is it solely manga/anime/etc world's or are tv series and movies, book series, the list goes on give us a glimpse of the sort of realm you'd like to explore first. then i' give a response based off that. As I'd like to reccomend something you know well enough to craft a story from.
the walking dead, as the girls are already used to the zombie it would be fine since fenrir still does not adapt well to the modern age, the lord of the rings or the hobbit, it can be useful since there are many different races and those that appear in the movies are not so strong, besides there are dragons and more that could help the girls to adapt to the powers they have. danmachi, there they can train in the dungeon and there are many races it wouldn't matter much if the girls are different lineages. just leveling a manwha, there are monarchs and rulers that the girls can use to steal their power or raise their lineage with theirs, the rulers almost look like angels, there is a dragon, wolf, demon monarch that could steal or take away the power of the girls .