as true as it is, there's more to the appeal of human domestication guide than "the fantasy for trans girls is to be loved unconditionally," it's that the affini can prove it. I'm certain there are people in my life who do love me unconditionally, but even then on some level it's hard to believe fully. it's impossible to prove a negative, "this person would love me no matter what" isn't something I could ever be comfortable testing anyway. "what if it isn't true?" a big part of being trans is having to justify your very existence even to well meaning people, and what happens when your justification falters?
and I think a big appeal to the affini that seems to be lost on a lot of people is how these stories tend to be from the perspective of "the person who is just about as against this as someone possibly could be." consider HDG proper, Elvira is against capture on a moral level for obvious reasons like "kidnapping is wrong" and "I deserve freedom," but she's also personally racist towards the concept of aliens. all of this forces the affini into a position where they can't just show "enough" kindness, to move from that position to one of love and trust, the affini are forced to show so much love and kindness that they prove beyond a shadow of a doubt that they really do care. they understand that behind every vicious word and lack of faith from their floret-to-be is a subtle hope that the world the affini promise is the real one. such a hope deserves nurturing at any cost; they deserve to know beyond a shadow of a doubt that it is really true. by assuming the worst case scenario, the affini prove the negative.
that's the real trans girl fantasy at play here; to be at your worst and for someone to love you anyway, to not have to feel like you're hiding some layer of your identity deep down that would ruin everything if it came out. your mistress saw the very core of your being and yet here you are, still wrapped in her loving embrace. you bared your teeth and gnashed at every helping hand along the way, and yet she still says she loves you. she still shows you love and affection beyond what you could have ever imagined. why?
and then at some point you just have to accept that it's true.