Everything is Invalid Due to Insufficient Firepower

After these days of getting along, Tanjiro did listen to Dan Lei's words.

After all, as a "mountain savage" from the Taisho period, Tanjiro figured anyone nearby who could read characters could call themselves a cultured person.

With Dan Lei's knowledge, he was at least at the doctoral level, and Dan Lei would occasionally teach Tanjiro little physics tricks to build goodwill, even teaching him the multiplication table, to the point where Tanjiro almost regarded Dan Lei as a master.

So, seeing that the demon was already pinned down by Dan Lei, Tanjiro very sensibly took Nezuko to the back of the temple to find tools and dig a pit.

Meanwhile, Dan Lei, with a sinister grin, directly moved this nameless demon to the yard outside, pondering where to start cutting.

But this demon was a chatterbox, even now that it was captured alive, it kept running its mouth.

"Hey, what the hell are you? What kind of sorcery are you using to hold me? Are you one of those legendary demon slayers? But why does your aura feel so weird? You don't seem human!"

Dan Lei never thought the day would come when a demon called him inhuman, so he decisively waved his hand, conjuring a sharp ice blade, and sliced off the demon's head, hanging it separately on a nearby tree.

Yet even after that, the demon kept yapping.

So, Dan Lei took out the paper and pen he'd made earlier with magecraft and recorded:

"The moment the head was physically severed, a small airflow output system was rapidly constructed in the damaged throat, proving that demons can consciously generate or modify organs within their bodies."

"Bleeding after decapitation lasted only three seconds, blood loss not too severe, regeneration ability stronger than an ordinary Dead Apostle, placing it at a high-level Abundance Monstrosity grade."

Done, Dan Lei casually cut open the demon's chest and abdomen to expose its organs, then recorded again:

"The heart is beating, but blackened, tissue structure clear. The esophagus and stomach show black, unknown patterns, speculated to be for effectively enhancing the absorption and conversion of magical energy from flesh and blood."

Watching Dan Lei's operations, even with its head detached from its body and feeling no pain, the demon was horrified.

After all, having a sentient being watch itself get disemboweled, even knowing it wouldn't die, still bred fear.

But without the threat of death, fear didn't amplify, and the demon turned that fear into anger, starting to curse Dan Lei.

Dan Lei's response was to completely seal the ventilation openings below its neck and all the holes on its head with ice. With no airflow, no matter how wide it opened its mouth, no sound could come out.

Finished, Dan Lei even flipped open its skull, looked at the still-living brain inside, and decisively scooped it out with an ice blade, freezing it and tossing it to the ground.

The demon, which had been moving moments before, instantly stopped all action the moment the brain was removed, its body ceasing to struggle. But soon, a new brain grew right inside the skull, and even the skull cap regenerated on its own.

So Dan Lei, recalling demons from the story that grew heads directly from their flesh, recorded again:

"Removing the brain temporarily halts all demon activity, but it will rapidly regrow a brain, and it doesn't necessarily have to grow from the head area."

Since this demon was very low-ranked, there was no point in looking for Blood Demon Art data on it.

And after regrowing its brain, the thing seemed to gain a bit of intelligence. Its head sprouted two arms and hands from below the neck, started clawing at the ice on its head, cleared its ears, and began cursing Dan Lei again.

Seeing this, Dan Lei promptly tied up its little hands with magecraft threads, resealed the holes with ice to silence it, and chopped off one of the demon's legs to test the real lethality of his magecraft against demons.

After a flurry of fireballs, lightning bolts, and ice shards, Dan Lei confirmed that his ordinary elemental attacks couldn't completely kill all of a demon's cells.

To kill a demon this way, he'd have to damage it until its internal energy was too depleted to regenerate, or else he'd be facing an infinitely proliferating mass of flesh.

Just then, a person suddenly emerged from the woods, speaking slowly:

"With methods like that alone, you cannot kill a demon."

This person was the one Dan Lei and Tanjiro had been seeking—Sakonji Urokodaki, the former Water Hashira of the Demon Slayer Corps.

He had arrived while Dan Lei was performing the craniotomy on the demon, and the spirit-form Kojiro Sasaki had informed Dan Lei immediately.

But Dan Lei had told Kojiro Sasaki to stay on alert and ignore him, so he'd watched until now.

In response to Sakonji Urokodaki's words, Dan Lei silently used the demon's blood to draw a magecraft circle, then cut off a fresh leg and tossed it in.

The next second, the magecraft circle activated, and the leg instantly turned to ash and vanished.

So Dan Lei smiled at Sakonji Urokodaki and said:

"It's not that troublesome. Monsters like demons still follow the law of conservation of energy. Drain the magical energy, and the flesh immediately disperses.

Of course, that's also because this demon is too weak. Its flesh binds energy with terrible efficiency and has little to begin with, so it drained dry in one go."

Done, Dan Lei turned back to the demon's body and added:

"Actually, elements aren't completely useless against demons. All ineffectiveness comes down to insufficient firepower."

With that, Dan Lei drew another magecraft circle under the demon's body using a bit of its blood, and a blue-white flame shot out.

This was a magecraft circle Aoko had taught Dan Lei for smelting metal when making puppets. In his past life, Dan Lei's limit was raising the flame temperature to just over 800 degrees, and many high-level puppet metal smelting jobs could only be done by Aoko herself.

But now, Dan Lei instantly raised the temperature to 2000 degrees. Though it consumed a massive amount of his magical energy and couldn't last long, it was enough to show off.

Under the 2000-degree heat, the demon's body instantly vaporized, and its bones rapidly carbonized into utterly dead matter.

At that moment, Kojiro Sasaki appeared on Dan Lei's orders and tossed the hanging demon head into the flames.

The moment the head burned up, the demon died instantly, and even the previously frozen brain on the ground turned directly into black ash.

Done, Dan Lei extinguished the magecraft circle's flame and said to Sakonji Urokodaki again:

"See, that's how you burn a demon to death directly.

Also, if you could draw down real heavenly lightning, it would definitely kill a demon.

And I've already tested it—elements can effectively kill off demon cells, weakening their defenses. That's the same principle behind why your Breathing Technique, when channeled through your blades with elemental properties, kills demons more effectively."

By now, Sakonji Urokodaki was drenched in sweat. If not for the mask on his face, Dan Lei would have seen his twitching mouth.

After a long silence, Sakonji Urokodaki came to his senses and gave a slight bow.

"Sakonji Urokodaki greets the foreign friends, Lord Dan Lei and Lord Kojiro Sasaki. Giyu Tomioka has already told me about you two—you are true people of extraordinary ability. Mr. Dan Lei's ability to burn demons to death with flames like Divine Fire left me utterly astounded. And Kojiro Sasaki is a master of the Heavenly Human Realm—this old man feels deeply inferior."

The part about not letting the demon make a sound is like deliberately blocking our throat with the root of our tongue, so that not a single sound can escape.