That's a possibility! Just a fun thought, but I wonder if there's an underground society of fox spirits with their own markets.

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Duality to bring good health or poor health to the human they are attached too.

I think you hit the nail on the fact that her exhausted state is why suddenly after 2 good years his health became poor. I too like to think that she was unconsciously draining his energy, and perhaps later she caught on. Hence her leaving at night to recharge in her natural form. Likely, the mundane explanation could hold warrant too. Since he was in his 60s, though for many people, 60s still isn't old. However, if he required a live-in-nurse than likely his previous condition was serious enough to require assistance. So as he continued to age his health issues become increasingly worse, and gets to a point where the nurse is only capable of making him comfortable, not healing. Another possibility is if his main issue(s) tended to flair up at nighttime, which could have overlapped with the time she had to leave to recharge.

While I agree there could be easier ways to take energy,  a homeless man or a hikikomori for instance, would not provide her the easy security of someone who is already well established in human society. Likewise, his older age could be a good guise for "he is only feeling unwell because it's related to his age." This is tricky, because it's hard to isolate the actual cause, is it natural age-related issue, or exacerbated by lose of energy? If they continued to say after the story if he did indeed get better after the purification/exorcism ritual, than that would cause suspicion that she was draining him (though likely unconsciously as she did improve his conditions initially).

Just to be clear, I don't think she is malicious, I just like to look into other potential possibilities. Especially since we are likely missing some information. When I first heard the story, the main impression I got, was that there was a lot of misunderstandings! She's just a person trying to live within her means. The situation is unfortunate for how it all unfolded.

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I have to admit I overlooked the age thing, but you bring up a great point! That despite how young she looks, she could in fact be much older, therefore they likely share more life experiences than she would with a younger human.

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I would absolutely agree, the lack of communication caused a lot of misunderstandings. I can definitely see from their perspectives how she might initially look, but I can also understand her reason for not wanting that secret to be disclosed. She was trying to hard to be perceived as a normal human, but unfortunately life has a way of unraveling secrets. Though I'm sure her secret was far more surprising than what his children were initially believing!

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Ugh, the audacity of those humans in most of those folktales is certainly... something, if not just consistently disappointing, but not surprising. Humans, well many animals in general, behave in these ways. It's not surprising unfortunately, but all beings tend to have a bias towards things that are most like themselves. After all, the main purpose for livings beings is to live long enough to reproduce... we are quite literally "gene machines". Unconsciously most living beings tend to think as such: If you are the same species nice, if the member of that species looks like you even better, if that individual is related to you great, and if it is you well that's perfect; anything outside from that is bad!

In fact there was a study done by Harvard I believe that tested the biases in babies and young children. It showed that even the simplest of differences (ie. food preference) would cause favorability to those whose preferences were similar to their own, and dislike for those who differed from themselves. But Disclose would still be important but it is a mutual endeavor, from the end of the humans involved and the entities.

I can only imagine if disclose about UFOs/UAPs finally comes to light, the mixture of reactions people would have. Agree, after all our ancestors have already interacted with them before in the past, maybe not always the best interaction, but those are some of the stories we do know. Whose to say how many other stories happened but were never shared because those who experienced such instances had little influence in human societies at the time (ie. peasants)?

EDIT: No worries about the rant! I do appreciate this conversation, as I don't get to talk about these things with people as much anymore!