Our next monster girl from Interviews with Monster Girls that we will be taking a look at is Yuki the Yuki-Onna.  As previously discussed, Yuki’s core body temperature probably runs somewhere between 86-90 degrees Fahrenheit.  And this fact will be at the core of what we will be discussing today.  So, if you haven’t figured it out, we will be talking about hyperthermia, and before you ask why not hypothermia, remember that I previously assumed Yuki would have a lot in common with echidnas.  That is because Echidna’s can have a body temperature as low as 41 degrees Fahrenheit so hypothermia is less of a concern for Yuki.

Increased Body Temperature

There are several terms to describe an increased body temperature, with each one covering a specific range of temperatures, with the more important two seen below.

  • Hyperthermia 100.9 to 104.0 °F
  • Hyperpyrexia 104.0 to 105.8 °F

Now I can’t say for certain what would constitute an elevated body temperature would be in Yuki, but if we use Echidna’s as a guide it is probably at or above 91.4 degrees Fahrenheit.  I came to this number after finding a study that Echidna’s can only dissipate 1/3 of their body heat through sweating at 91 degrees Fahrenheit.  At this temperature the Echidna’s were struggling to maintain a normal body temperature. 

As a reminder there are various symptoms of an increased body temperature in humans, with the severity of the symptom being related to the degree the body temperature is above the normal human level of 98.6 F.  The first of these is heat fatigue, which occurs from exposure to high temperature and often includes dehydration.  The symptoms are the typical ones you would expect from being outside in the heat: excessive sweating, exhaustion, flushed or red skin, muscle cramps and headaches. 

If the body temperature continues to be elevated and the person continues to get dehydrated heat exhaustion can occur with all of the symptoms of heat fatigue plus cold, pale, wet skin, weak pulse, nausea, dizziness, and intense thirst.  If the body temperature remains elevated heat stroke can then occur with all of the previous symptoms (except sweating which has stopped by this point), and the following disorientation, blurred vision, irritability, lack of coordination, and loss of consciousness.  Of course, if the body temperature continues to remains elevated past this point it can result in organ failure and death.

What does this all mean for Yuki?  Well, I think the most important thing for Yuki, outside of not living in hot and humid places, would be some sort of medical ID bracelet or tag.  This is because some of the symptoms of hyperthermia can also look like symptoms of hypothermia, and when combined with Yuki’s naturally low body temperature, it could cause medical personnel to treat Yuki for hypothermia trying to raise her body temperature when in fact, she needs her body temperature to be lower.


As I was searching for something else to discuss about Yuki besides the obvious hyperthermia, I came across something interesting.  The echidna’s ability to enter REM sleep is temperature dependent.  You might be asking why does this matter?  It matters because if Yuki has the lower body temperature of echidna’s, there is a good chance she has other elements of their physiology as well, which includes the brain.  Now REM sleep or rapid eye movement sleep is very important beyond the fact that this is the portion of sleep where we dream vividly.  REM sleep is thought to play a role in memory and neural development, though these are still currently being researched.  Known and unknown roles aside, REM sleep is important because of what happens when we go without it:

  • Slowed reaction time
  • Increased anxiety
  • Irritability
  • Hallucinations
  • Increased appetite
  • Decreased mental functions
  • Weakened immune system

Circling back to what I said earlier, Echidna’s only enter REM sleep when the ambient temperature is between 59 to 82 degrees Fahrenheit, with the preferred temperature being around 77 degrees Fahrenheit.  Thus, it is going to be a bit harder for Yuki to enjoy REM sleep given the temperature range she must stay within.


A bit shorter than usual, but I hope you enjoyed another romp through anime science.

Author: Anime Science 101 is an American science teacher with eight years of experience working in high school and middle school classrooms. His last teaching job was overseas in Mongolia, where he had easy access to the home islands of Japan, which went to twice for a total of 9 weeks spent travelling the country. While his main background is Biology, specifically all things related to medicine due to two years of medical school, he can teach all aspects of science, including anime science.

2 thoughts

  1. So how does Yuki produce ice? Wouldn’t the ability to cool down her enviroment be relevant for hyperthermia? Her biology might have ways to cool herslef down other than sweating. We’ve seen her cry ice, as far as I remember, and we’ve also seen her cool down her environment significantly. I think that’s where the analogy to echindnae breaks down a litte. (I’d definitely prefer a cooling echidna to an air coditionor, though. That would be one useful pet.)

    1. Animescience101 chimming in here. I covered that in a post on my own blog so I didn’t put the answer in this one as well.


      TLDR- Yuki creates ice using an endothermic salt dissolution reaction aka those instant ice packs that you break and get cold real fast. This happens through mixing the salt with water. 1- don’t know the exact chemicals because her ice is never analyzed in the anime. 2- there are a lot of them and some are not compounds you want in the body.

Leave me a comment and make my day!