I really have liked this series, and still do, but there have always been a number of weird elements at or just below the surface that combine into an unsettling subtext (and sometimes text).
1) Mel’s status as a furry displaces our normal assumptions and creates a great deal of uncertainty about a lot of fundamental premises. Mel is certainly young, but in beastkin terms, how young? In flashbacks to the orphanage (?), Mel’s classmates seem to be at least late adolescents, and with no idea of their lifespan/developmental pattern, we also have no idea of how much of Mel’s apparent childishness is due to her age and how much is her personal naïveté and inexperience.
2) In the context of the story, Mel’s collar seems to be a voluntary personal ornament, which doesn’t change the fact that it also reads as sex fetish gear.
3) What is Mel even doing there in the first place? There’s certainly a master-servant relationship, but Mel’s role working in the house seems to be entirely voluntary. And we have almost no idea of the wider cultural practices concerning the beastkin—what even counts as normal in this world?
None of this is to say anything about the morality of the relationship one way or the other, but just to say that this has always been a loli d/s story. And it’s always been incredibly cute.