Interviews with Monster Girls- Yuki the Yuki-Onna
Yuki is the second to last monster girl we are introduced to in Interviews with Monster Girls, and the only monster based solely on a Japanese myth. The Yuki-onna or snow woman is a mysterious creature who lives in cold snowy places, and is either a benevolent spirit, or a murderous demon depending on the story. Different locations in Japan each had their own version of the Yuki-onna. In some she comes into the village to become the wife of one of the single men, and they remain happily married until he prevents her from leaving or forces her to bathe. In either case she leaves in a shower of snow petals. In another version of the myth the Yuki-onna will hug little children as they trudge through the snow, slowly freezing the child to death. As a result, mothers would not let their children out at night to avoid having a run in with a Yuki-onna. In the final version of the Yuki-onna myth she comes knocking on the door of a logger or hunter’s hut asking for water. If the men give her water they die, but if they give her hot tea, it drives her off.
I particularly enjoyed how Interviews with Monster Girls was able to combine the myths of the Yuki-onna into the character development of the character Yuki. Where Hikari and Machi are comfortable with their monster girl abilities, and Sachi has learned how to live with hers, Yuki is actually scared of her powers. Initially she is very afraid of her powers, and that she might actually freeze someone to death by accident. While the anime does not give a plausible reason for her powers, there is a way she could theoretically have some of the abilities seen in the anime. Like the other monster girls, Yuki is at her core a human, with some special powers. This means that her physiology is close to human. While this does limit an exploration of her powers a bit, it also makes it easier since I have a starting point.
Lower Body Temperature
Hikari does not like the heat, and once she meets Yuki, Hikari loves to use her as a sort of mobile air conditioning unit. The normal human body temperature is 98.6 degrees Fahrenheit (37 degrees Celsius), so for Yuki to feel cold to the touch her body temperature should be significantly lower than that. This creates a problem because hypothermia (lowered body temperature) begins at 95 degrees Fahrenheit; even severe hypothermia, which begins at 82.4 degrees Fahrenheit, wouldn’t make you a very effective mobile air conditioner. The second problem is that a human would be unconscious at that body temperature.
While Yuki is human, she is also a monster girl, which means her physiology might be a bit different, and there are mammals with extremely low body temperature. A case in point the is Echidna, also known as a spiny anteater, which is part of a small group of mammals known as monotremes. Monotremes are mammals that lay eggs. Currently there are only five species of monotremes: the platypus, and 4 different species of Echidnas. There are many traits that make the Echidna unique, but the one that matters the most in Yuki’s case is that their normal body temperature runs between 86 to 90 degrees Fahrenheit. While that is not that cold, the Echidna’s body temperature can decrease to 41 degrees Fahrenheit under certain conditions, and 41 degrees Fahrenheit would make a great mobile air conditioner. This means that Yuki’s thermoregulatory system probably has much more in common with an Echidna’s than normal humans.
Lack of Sweating
Hypohydrosis, or a lack of sweat production, is another trait that Yuki says she has as a result of being a Yuki-onna. The lack of sweat production can be caused by genetic conditions, certain drugs, diseases, and physical injury. In any event, the lack of sweating causes the body to overheat, leading to hyperthermia, which if left untreated is a fatal condition. You can find more about hypohydrosis here in my post about Shishio Makoto from Rurouni Kenshin:
I like how the anime has a lack of sweating as a trait of Yuki-onna’s because it fits with the characteristics of a short beaked Echidna, which does not actually sweat. This just leaves us with more evidence that Yuki-onnas evolved from Echidnas. It also begs the question as to just what kind of research did Petos do while writing the series?
Now the question that you have all been waiting for, how does Yuki create ice? While the anime does give an explanation as to when Yuki creates ice, (while she is nervous), it does not explain how the ice was actually made. If you saw my talk at Otakon 2017, you will remember that I did not have an answer for this, but one of the attendees did mention the possibility of endothermic salt dissolution. For all of you non-chemists out there, what endothermic salt dissolution means is that some salts will cause a drop in temperature when dissolved in water. It’s how many instant ice packs work. There is a bag of salt and a bag of liquid inside the pack and when the bags are broken and the contents mixes, you get instant cold. This happens because the energy needed for the chemical reaction to happen is absorbed from the environment, making the surrounding air or water colder.
Essentially the little sweat that Yuki does release would have to contain the chemicals needed for these reactions to occur, and since sweat does contain some salt it is a not a very big leap to think that the sweat of a Yuki-onna might contain salts different from that of a normal human. I believe this is what Tetsuo was thinking when he tried to take some of the ice Yuki created and have it analyzed. Sadly, Yuki found that a little too embarrassing and prevented the analysis from happening.
I can think of two endothermic reactions (reactions that absorb heat and make things cold) that could be happening. Reaction number one is ammonium chloride and barium hydroxide, which when mixed can lower the temperature enough for water to freeze as seen in the video below.
Ba(OH)2 + NH4Cl àBaCl2 + NH3 + H2O
While this would lead to the creation of ice, I do not like this particular reaction because it will release ammonia. Ammonia has a rather strong foul scent (think cleaning solutions), and well no one ever complains about Yuki smelling bad, so I don’t think this is the one. The second and more plausible reaction is mixing of ammonium nitrate and water, which does cool water significantly and in the right amounts can cause it to freeze.
In either case the creation of ice to cool the body would not be a defensive mechanism, but a way for the Yuki-onna to stay cool in the hot weather. With the inability to sweat very much, the little sweat Yuki does release would have to cool the entire body, and covering her skin in ice crystals would do just that.
I hope that you have enjoyed my romp through the monster girls of Interviews with Monster Girls. I know that there are many monsters in the Daily Lives of Monster Girls and I will try and explain the few that I can in that anime in the future.
Thanks for reading and please leave any comments or questions below.