Fabre in Sacheon’s Tang

The mention of both pufferfish and shellfish toxins appearing together made me tilt my head in confusion.

It was only natural. As far as I knew, no venomous creature used both toxins at once.

‘If it’s pufferfish venom, it would be tetrodotoxin. And if it’s shellfish, then... since the elders of the Tang Clan confirmed it... it’s probably saxitoxin rather than Vibrio.’

Pufferfish venom is undoubtedly tetrodotoxin—nearly all toxic puffer species contain it.

As for shellfish toxins, the possibilities narrow down to either Vibrio bacteria or saxitoxin. But if the Tang elders labeled it a deadly poison, then Vibrio was unlikely.

This era doesn’t yet distinguish clearly between poisons and bacteria, but unlike Vibrio, which is destroyed by heat, saxitoxin retains its toxicity even when cooked. So if they called it a deadly poison, chances are it was saxitoxin.

‘If the Tang elders called it deadly, it must’ve been that serious.’

So why do I insist there are no creatures that use both?

While tetrodotoxin is most commonly associated with pufferfish, many other organisms use it too—blue-ringed octopuses, some sea snails, a few crab species, vipers, salamanders, toads, frogs, starfish, and certain flatworms.

Some produce it themselves, while others accumulate it from symbiotic bacteria living on their skin.

But saxitoxin, although found in some shellfish, is not produced by the shellfish themselves or their symbiotic bacteria.

It originates in marine dinoflagellates. Shellfish and crustaceans accumulate it after feeding on these toxic algae, and humans get poisoned by eating contaminated seafood.

So, if someone eats cooked shellfish and dies?

Then it’s almost certainly saxitoxin.

Which means there’s no known case of any creature using both toxins actively.

One is a defensive poison used by marine and amphibious species.

The other is an environmental accumulation—stored in the body, not produced.

No known creature uses both toxins aggressively.

But if we think about the similarities between the two, there is room to suspect they were combined artificially.

”The victims died from cardiac arrest, didn’t they?”

”That’s right.”

”Because both toxins shut down the heart?”

”Yes, Hwa-eun.”

My foster father confirmed it, and Hwa-eun seemed to recognize the toxins’ effects.

Indeed, both tetrodotoxin and saxitoxin paralyze the heart—they are neurotoxins.

Being neurotoxins, they cause paralysis, eventually halting the heart and leading to death.

If we compare their potency: saxitoxin’s median lethal dose is 0.57 mg.

Tetrodotoxin? About 2 mg.

That’s a difference of more than fourfold.

However, their mechanism of action is similar.

The human body runs on tiny electric currents.

To send signals for muscle contractions, stimuli, and heartbeat regulation, the body relies on sodium ions.

Both tetrodotoxin and saxitoxin bind to sodium channels and block sodium influx.

This halts nerve transmission, paralyzes muscles, stops breathing, and ultimately causes death by cardiac arrest.

And here’s what’s fascinating—when combined, the effect is immediate and deadly.

‘Basically, a neurotoxic cocktail.’

Which led me to believe it likely wasn’t a new venomous beast or spirit creature.

The perfect synergy between these two poisons suggested it was the work of someone with deep toxicological knowledge.

I asked my foster father,

“You couldn’t find the culprit, but you assumed it was a new Five Venoms Sect creature because of the pufferfish and shellfish toxins?”

”Yes. That’s what the elders said. There were no signs of any beast, but the poisons used were consistent with venomous creatures. So they suspected a new type.”

As I expected.

This era doesn’t know that saxitoxin comes from dinoflagellates and is accumulated in shellfish.

They likely assume the shellfish produce it themselves.

And from there, it’s easy to imagine a new venomous beast or spirit creature was responsible—especially when no beast traces were found.

I shook my head.

“It could have been a person.”

”A person? But no one saw anything—not a single trace.”

My foster father had dismissed the possibility of a human culprit because there were no traces.

So I explained why I thought a person was more likely.

“Yes. If it were a Five Venoms Sect beast or spirit creature, it would probably be one of their artificially modified venomous species. And those are always based on existing poisonous creatures, aren’t they?”

“Yes, that’s true.”

“Right. And to my knowledge, no creature uses both pufferfish and shellfish toxins together.”

“What if it’s a creature you don’t know about?”

He suggested the possibility that there might be one I didn’t know.

But I found that extremely unlikely.

“Almost zero chance. And I have another reason to think it’s human. Both tetrodotoxin and saxitoxin share one trait—they paralyze the limbs, lock up the body, and ultimately stop the heart.

But when used together, they create a powerful synergistic effect.”

“Synergy?”

“Yes.”

“Is that really true, So-ryong?”

Even Hwa-eun looked surprised—this must’ve been something not even she knew.

In the world of venomous creatures, toxins are typically used alone for potency. And the Tang Clan favors its own custom blends.

But when combined, these two poisons kill fast.

Where to?

To the afterlife.

Both poisons interrupt sodium ion transport—but in different ways.

Tetrodotoxin blocks the outside of the sodium channel.

Saxitoxin blocks the inside.

So when both are applied, the signal system fails completely—no nerve impulses get through.

This effect was even studied ~Nоvеl𝕚ght~ in modern research.

‘Why did someone mix the two? There are lots of curious people in this world like me, I guess.’

Thinking back, I figured someone else had gotten curious, too.

“Yes. Pufferfish toxin and shellfish toxin both paralyze the body. Saxitoxin works from the inside, while tetrodotoxin works from the outside. Together, they cause instantaneous paralysis and death.”

“I didn’t know that. I thought they were just similar.”

Hwa-eun looked amazed as she finally understood, and then my foster father spoke again.

“So you’re saying... there’s a high chance a human was behind this?”

“Yes. My guess is that it was someone at the Flower Realm level.”

“F-Flower Realm!?”

My foster father jumped at the mention.

It was only natural—this meant an expert-level master had emerged on the enemy side.

To my knowledge, a Flower Realm master was on par with the Three Sovereigns and Five Emperors of the martial world.

And our side had no such figures here.

“Then this is serious. We need to inform the Murim Alliance and urgently summon at least one of the Five Emperors...”

He meant we needed to call in someone strong enough to hunt this enemy down.

But I smiled and reassured him.

“There’s no need to worry too much. We already have two Flower Realm masters here.”

“Two!?”

My foster father was stunned.

Well, it’s technically three.

But I decided to keep that part to myself.

***

As expected, the wedding was postponed.

With people dying and the front lines retreating, if I were to get married now, it would only crush morale.

Life’s unfair, sure—but when one person dies fighting with nothing but dirt in his hands while another, born with a golden spoon, celebrates a wedding? Of course morale would nosedive.

So we decided to hold the wedding after this problem was resolved.

How?

Noblesse oblige.

A moral obligation that comes with status.

I’d take it upon myself to step up.

Only after I resolved this crisis in spectacular fashion—and when people cheered my name—would I hold the wedding.

Because I’m a man of the people, no?

”Right, if there are two Flower Realm experts here, even if the enemy is at that level, it shouldn’t be hard to take them down. I’ll inform the Murim Alliance that you’ve both reached the Flower Realm and will be acting. That should boost morale.”

”Understood, Father.”

Before heading to the bamboo outposts that had been built for night patrols, Hwa-eun and I went to examine the bodies.

I hadn’t intended to go—but Hwa-eun insisted on confirming everything with her own eyes.

Just to be sure, she said, we should verify the exact poisons used.

‘The elders already handled it. I’m sure they did fine. Hwa-eun’s so meticulous it’s almost excessive.’

Still, I had no choice but to follow along. Even though the idea of facing corpses unsettled me.

We arrived at the scene, led by Tang Clan elders who looked none too happy, their expressions tight.

”These are the bodies.”

”Thank you for your work.”

”It was nothing. I heard the news—you reached the Flower Realm?”

”Yes.”

”Congratulations. We always believed you’d reach the heights someday.”

”Thank you.”

These elders were guarding the bodies, and from the smiles on their faces, it seemed the news had reached them through the warriors of the Venom Blood Squad.

Hwa-eun, however, remained cold and indifferent.

‘They were so hard on her for being a girl before...’

‘Let it go, Hwa-eun. It’s all in the past.’

She was probably still holding onto a bit of resentment, so I tried to reassure her silently.

But regardless of her feelings, Hwa-eun was always thorough. She pricked the corpse with a needle and confirmed the type of poison.

“It’s definitely pufferfish toxin and shellfish toxin.”

“The ratio?”

“There’s much less of the shellfish toxin.”

“How much less?”

“There’s about four times more pufferfish toxin than shellfish.”

“Then it’s almost certain this was the work of a human. Pufferfish toxin is about four times weaker than shellfish toxin.”

Since saxitoxin is four times more potent than tetrodotoxin, using them in this ratio meant the poison had been carefully balanced to a 1:1 lethal dose.

That’s the ratio that kills most efficiently.

And no creature can balance dosage like that—not unless it’s human.

‘This only confirms my theory.’

I was becoming more and more certain it was a person.

Just then, while examining the body, Hwa-eun seemed to spot something.

“Hm? What’s this?”

She pointed at the corpse’s mouth, now pale in death.

Why was she even checking the mouth?

Frowning, I leaned in—and saw something white inside.

“Looks like leftover noodles.”

“Does it?”

A clump of soggy noodles, half-decomposed, was stuck inside the mouth. I brushed it off casually and covered the body again.

I didn’t want to keep looking at the corpse’s face any longer.

For some reason, the mouth was frozen open and the eyes had never closed, suggesting the body had been found long after death. It was deeply unsettling to look at.

”Everything checks out, then. Just like we heard. Let’s catch the bastard tonight and avenge them.”

“Yes, So-ryong.”

‘We’ll avenge you. May you find peace in the afterlife.’

I swore it silently.

***

Night fell quickly.

We moved swiftly toward the border zone, now with Gun Hye-rin joining us.

Of course, we also brought Sister Jeokwol, Cho, Yeondu, Hyang, Hongdan, Moji, Soji, and even Heukhwa and Baekhwa.

When we reached the area we had scoped earlier during the day, we saw the bamboo towers rising along the border.

In my past life, these would be guard posts. I focused my inner sight—and could see warriors moving tensely inside the outposts.

The Murim warriors who had previously pulled back had now reoccupied them, likely to draw the enemy out.

No one had been killed during daylight, so they had taken the opportunity to retake the guard posts.

Hovering mid-air, I pointed down and signaled.

[We’re nearly at the area we checked earlier. As planned, let’s move to our individual hiding positions.]

[Understood.]

[Got it, So-ryong.]

We would each conceal ourselves in a specific spot near here.

The area we chose for tonight’s ambush was among the bamboo towers along the border—specifically, the section directly ahead of us, where previous deaths had occurred.

To the left ran a wide river; to the right stood a mountain.

No deaths had occurred at the outpost atop the cliff beyond the river. But between that river and the mountain, in twelve outposts—people had died.

So we decided to hide in this zone.

When you reach the Flower Realm, the first major change is heightened Qi perception.

If another Flower Realm master appeared, we would absolutely notice.

We split the twelve affected towers into three groups of four—each group watched over by a team of us.

I landed near the mountain, dropping off Gun Hye-rin and Yeondu in the grass.

[Remember, if the enemy shows up, your job is to trap them—don’t let them escape. Then call the others.]

[Understood. But I borrowed a sword. I doubt I’ll need backup.]

She had borrowed a sword—probably because she expected to fight a Flower Realm master.

She gave a proper reply... but something about her tone made it clear:

She fully intended to handle this alone.