These days, when reading popular martial arts webtoons, you often come across protagonists or exceptional masters with particularly unusual traits.

Two notable examples are the Celestial Killers (天煞星) and Nine Yin Meridians (九陰絶脈).

One is depicted as a being destined to disrupt the world from birth, while the other is born with immense yin energy but is unable to live long due to this trait.

Of course, neither of these traits actually exists in real medicine. However, it's interesting to consider that ancient people may not have completely fabricated these concepts without any basis.

From a modern medical perspective, there are real phenomena that might feel similar.

The Celestial Killer is typically portrayed in martial arts as someone born with a murderous aura. From a young age, their parents or those around them die, or they become embroiled in significant events, and they themselves live amidst fighting and death.

In reality, there is no such thing as a Celestial Killer born with a fate to kill. However, it is true that people are born with different temperaments.

Factors such as impulse control, fear response, aggression, and risk-taking tendencies are influenced by genetics, brain development, and environmental factors.

When faced with the same danger, some people may become extremely frightened and flee, while others may remain relatively calm or even move toward the danger.

If ancient people observed individuals with such extreme temperaments, it's easy to imagine them saying, "That person is born with a murderous aura."

The Nine Yin Meridians are a bit more intriguing.

In martial arts, those with Nine Yin Meridians are usually depicted as having excessively cold and weak bodies.

They have cold hands and feet, are extremely sensitive to cold, have pale faces, and tire easily.

In severe cases, they are said to not live past a certain age. Conversely, it's also common for them to gain incredible martial arts skills when encountering special internal cultivation methods or elixirs.

While there is no disease called Nine Yin Meridians in reality, there are certainly people who exhibit similar symptoms.

For example, those with hypothyroidism may be extremely sensitive to cold, feel fatigued, and have a slowed metabolism.

People with severe anemia also have pale faces, cold hands and feet, and tire easily with minimal exertion.

In more extreme cases, there are rare genetic disorders present from birth that affect specific enzymes, metabolic functions, the heart, or the immune system.

Particularly, the "cold constitution" described in ancient medicine does not correspond exactly to any single modern medical condition.

When various factors such as anemia, nutritional status, thyroid function, blood circulation, and the autonomic nervous system overlap in one person, they can indeed become much more sensitive to cold and physically weaker than others.

Thus, it's interesting to reinterpret the Celestial Killers and Nine Yin Meridians of martial arts in a modern context.

If the Celestial Killer expresses extreme "temperament" in humans, the Nine Yin Meridians are more about creating a mystical trait from a naturally weak body.

However, in martial arts, there's an additional element.

If a weakness is too strong, it can become the seed of tremendous ability.

A person destined to die due to Nine Yin Meridians may encounter exceptional martial arts and become the greatest in the world, while someone fated to see blood their whole life due to being a Celestial Killer learns to control that murderous aura and becomes a top master.

In reality, such explosive internal energy does not occur.

However, it is true that individuals vary significantly in genetic factors such as temperature regulation, muscle composition, pain sensitivity, stress response, endurance, and recovery.

To wrap it up in a more engaging and thought-provoking way, one might say:

Ultimately, the appeal of martial arts seems to lie in its grand exaggeration of the "inherent differences" in humans that clearly exist in reality.

Even if it seems like everyone is born the same, some are extremely sensitive to cold, some can stay up all night without issue, some are very fearful, and some remain oddly calm in dangerous situations.

Modern individuals might respond to these differences with blood tests, hormone checks, and genetic analysis. However, ancient people explained them through yin and yang, the five elements, qi, and meridians.

And martial arts authors didn't just sprinkle a bit of imagination on top; they poured it in with a ladle.

Those with particularly cold hands and feet become Nine Yin Meridians, while those with rough personalities and a sense of murderous aura become Celestial Killers.

Then, when an exceptional master appears and says, "This child will have a hard time past twenty," the story is complete.

Of course, the likelihood of discovering a trait like Celestial Killers or Nine Yin Meridians in reality is nonexistent.

It's unlikely that a doctor would look serious and say, "Sir, you have Nine Yin Meridians" after a blood test.

However, there is a reason why such stories have felt plausible to people for hundreds of years.

It's because people are indeed born slightly different from one another.

Modern medicine explains this through genetics, the nervous system, hormones, and metabolism, while martial arts simply referred to it as Celestial Killers and Nine Yin Meridians.

In that sense, martial arts may not have created completely absurd tales, but rather discovered small differences in reality and added about a hundred years of internal energy to them.