Reflection and Analysis

Demon Slayers - The Junk Science of Demon Slayer Marks (7/12/21)

Note - I spoiled myself by looking at the wiki for Demon Slayer, so this contains spoilers.

I'm writing Demon Slayer fanfic despite having only seen the Anime and read a few small parts of the Manga yet I'm looking into certain details on the wiki so I can be canon compliant except for the places which need a bit of fix-fic and I started looking closer at the Demon Marks particularly since I'm thinking in nixing them for my rewrites, or noting that it is a misconception that it kills when it kills and I got this bit of information.

"The Demon Slayer Mark can only appear in Demon Slayers that survived the life-threatening conditions of having a heart rate over 200 bpm and a body temperature over 39° Celsius (102.2° Fahrenheit)"

The fact they die at age twenty-five must be true because Shinobu confirmed that "the conditions for unlocking it alone was deadly even for a Hashira" except...

I'm laughing my head off at this one because I decided to look into this and one of the first things was I found the following line from healthline in an article written by Dr. Angela M. Bell called Why Do Athletes Have a Lower Resting Heart Rate?

"However, an athlete's heart rate may go up to 180 bpm to 200 bpm during exercise."

Like, we've a doctor here saying that is normal. Mind you, it's not a bpm that an athlete wants to keep up for long periods of time. The article also touches upon the fact the calculation is based on an old school calculation method, so subtracting the Hashira's ages from 220 doesn't work. This is also supported by Heart Rate Records for topend sports, but Demon Slayers would fall into GASP - the athletic category!

Then there's the "fever" which according to "What's considered a fever and when to see a doctor" for OSF HealthCare by Laura Nightengale, that would still be considered a low grade fever which "usually require treatment". It's when it starts getting over that, "it can be a sign of a more serious infection".

It's not actually "life threatening" like the writer has Shinobu claim. Not unless there are other symptoms going on. Talk about junk science, but it didn't take me long to figure this out. According to Providence ExpressCare's article "Fever in Adults Quick Overview", it's not until the fever gets to be 104 or higher that it is considered high-grade and thus considered dangerous. This doesn't mean that intermediate fevers shouldn't be taken seriously, but they're not life threatening as Shinobo claims.

As I said, junk science.

This isn't to say it can't be life threatening, but the circumstances and other factors need to be taken into consideration - though, I also have to wonder how they even know this is what causes it to manifest when - oh, it's during the 1910s that takes place which means - well, reading there's an article for Frontiers in Physiology by George E. Billman called "Heart rate variability - a historical perspective" that says she shouldn't have anywhere near that kind of knowledge for BPM.

Maybe fevers, but even then - it's inaccurate, but also not something that would be measured during the middle of a fight so how did they come to the conclusions that is what makes it first appear? They can't know that, because they're not measuring it in the first place, and even if that is the activation points - it's still so ever iffy.