Imo I don't particularly care about the morals of the thing as long as they're well done. If they're some variant of evil but treat you right, that's something that can build attachment. The "I can fix them" thing. Countless characters and love interests have done that. Kas does that, even though she doesn't really do much "evil". Primary issue with the kitsune is that's how they seem to think it's being done, when at best it's not a bad boy/girl that loves the pc/"you", the type that blocks attacks for you and says "hands off my man/girl". You can make seriously vile characters relatable or attachable with the right amount of love. But it comes off far more like a blatantly abusive Harley Quinn/joker type deal where they'll toss a "I miss you" but then the "your opinion doesn't matter". She acts one way when you're alone and one way around other people, but it's not a mask and she doesn't say "I'm sorry I had to say that, you're bae forever I just didn't want him to feel bad or kill him outright", she just says it factually and your chars supposed to take it.
You take on their den, nobody cares, you save her from eternal isolation after she's been alone for who knows how long, she pops out, doesn't care, you're her ho and should be thankful for that, and if people trash talk you, well that's rude, but of course, true. She acts too perfect for someone that went through all that. Compare to brienne you get cake for and take care of and then is loyal af and doesn't take anyone talking shit.