The flames Dan Lei had used to incinerate the demon completely with one hand had truly impressed Sakonji Urokodaki.
Given the industrial capabilities of the Taisho era, how could the Demon Slayer Corps possibly produce flames reaching 2,000 degrees? They'd be hard-pressed to produce flames reaching even 1,000 degrees.
In the anime, the flames wrapped around Flame Pillar Kyojuro Rengoku's sword couldn't trigger a Scarlet Blade, proving they weren't hot enough to make the Nichirin Blade's metal glow red.
The original story had a method of striking Nichirin Blades together to create a brief moment of high heat. In other words, the temperature needed to make the Nichirin Blade's metal glow red couldn't be too high, or that method would never have reached it.
Although no one knew exactly how hot the metal of a Nichirin Blade had to get before it turned red, ordinary metal became red-hot at around 500 to 800 degrees. Judging by that, the temperature required to forge a Nichirin Blade couldn't have exceeded 1,000 degrees by much. Otherwise, with the technology of that era, how could ordinary craftsmen have produced so many Nichirin Blades in bulk?
The Demon Slayer Corps had surely tried burning demons to death before, and they surely hadn't succeeded.
So Sakonji Urokodaki couldn't begin to imagine Dan Lei killing a demon with flames reaching 2,500 degrees. He immediately thought it was Divine Fire.
As for Kojiro Sasaki, Sakonji Urokodaki hadn't even noticed when he'd appeared. Even standing right in front of him, Kojiro gave off no detectable presence. Naturally, Sakonji accepted that this was the legendary state of Oneness with Nature.
Seeing that Sakonji Urokodaki was convinced, Dan Lei naturally adopted a friendly manner. He returned the greeting and said,
"Mr. Sakonji Urokodaki, I've heard a great deal about you.
I imagine Mr. Giyu Tomioka has already explained things to you. We'll be imposing on you for a while."
Since Dan Lei wasn't putting on airs despite his strength, Sakonji Urokodaki didn't act stiffly as he had when he first met Tanjiro. He immediately said that Dan Lei's willingness to study demons was a good thing, and that providing a place to stay was the least he could do.
While Dan Lei and Sakonji Urokodaki exchanged pleasantries, Tanjiro and Nezuko had already buried the people who'd died at the temple.
Nezuko was very strong, and there were ordinary tools like shovels in the temple's backyard, so they finished quickly.
After burying the dead, Tanjiro said a customary prayer and went to find Dan Lei. He happened to see Dan Lei speaking with a man wearing a Tengu mask.
Seeing that Tanjiro had finished burying the dead, Dan Lei naturally introduced him to Sakonji Urokodaki.
"Mr. Sakonji Urokodaki, this is the boy, Tanjiro. Nezuko is behind him. I can vouch for her—she hasn't lost control once in the past few days."
However, after hearing Dan Lei's words, Sakonji Urokodaki didn't immediately respond. Instead, he slowly walked up to Tanjiro and said,
"I'm Sakonji Urokodaki. Tanjiro, tell me: if your sister ate a person, what would you do?"
Tanjiro was naturally taken aback by the question. He couldn't accept the thought of his sister eating someone, because he knew that eating people was evil, but he couldn't bear to hurt her either.
That moment of hesitation earned him a slap from Sakonji Urokodaki, followed by a scolding.
"Not good enough! You took too long to decide! Your whole body is screaming hesitation! You aren't truly resolute!
"If your sister eats someone, you have only two things to do: kill her, then take your own life! That's what it means to have a sister who's become a demon.
"Remember this: never let such a thing happen. Never let your sister take the life of an innocent person!"
Tanjiro was stunned by the slap, and instinctively looked toward Dan Lei, who'd become someone he could rely on over the past two days.
But Dan Lei was just as stern.
"Tanjiro, don't look at me.
"Mr. Sakonji Urokodaki is right. If your sister eats someone, the best thing to do is kill her before that happens.
"If you can't do it, I will.
"If I'm no longer by Nezuko's side when it happens, I'll come back and kill her as soon as I find out.
"Then I'll leave myself a scar that will never fade, so I'll remember what happened for the rest of my life.
"And stop looking to me for everything. I'm only passing through your life. One day, I'll leave. You have to learn to stand on your own. Otherwise, when I'm gone, will you ask Nezuko, who can barely express herself right now, what to do?"
Dan Lei's scolding cleared Tanjiro's head. He immediately stood up straight and answered seriously,
"Yes, I understand!"
Seeing that Tanjiro had understood his point, Sakonji Urokodaki continued,
"Giyu Tomioka has told me about you and recommended you for the Demon Slayer Corps.
"So I'll follow the usual procedure and test whether you can become a swordsman who kills demons.
"Put your sister in the box and carry her as you follow me."
After that, Sakonji Urokodaki also said to Dan Lei,
"Lord Dan Lei and Lord Kojiro Sasaki, please follow me as well."
With that, Sakonji Urokodaki began jogging along a country path.
Sakonji Urokodaki was obviously testing Tanjiro, so he wasn't running very fast. With the physical abilities of a Sustainer Dragon Clan member, Dan Lei kept up with ease. As for Kojiro Sasaki, he found the pace too slow and turned into his Spirit Body.
Tanjiro, meanwhile, had to run at full speed while carrying the box just to keep up.
But Tanjiro was used to carrying loads of charcoal down the mountain to sell and then returning home the same day, so his stamina was up to the task.
And whenever he felt he couldn't keep going, he thought of Nezuko and used his love for her to encourage himself to press on.
And so, running from dawn until noon, then from noon until dusk, with only a few stops for food and water, Tanjiro made it to the front of Sakonji Urokodaki's house.
Actually, for an ordinary Demon Slayer Corps swordsman selection, Tanjiro would have passed by this point.
However, Sakonji Urokodaki had already lost thirteen students during the Final Selection since becoming a trainer.
That had made Sakonji doubt his ability to teach and become even stricter in selecting students. After all, sending out someone who wasn't strong enough was tantamount to sending them to their death.
So Sakonji Urokodaki still had one final test for Tanjiro: he had to run down from a mountain filled with traps and reach the house alive within the time limit.
This time, however, Tanjiro wouldn't need to carry Nezuko. Dan Lei had Kojiro Sasaki appear and watch over things at the foot of the mountain, while he went up the mountain with Sakonji Urokodaki.
Dan Lei hadn't gone up the mountain just to watch Tanjiro's test. After Tanjiro began, as they made their way down, he said to Sakonji Urokodaki,
"Mr. Sakonji Urokodaki, forgive me for being presumptuous, but could you teach me the Breathing Technique while you're teaching Tanjiro? I'll repay you with my research materials on demons."
Dan Lei's words made Sakonji Urokodaki stumble, nearly taking a spill on level ground. Once he'd steadied himself, he gave a somewhat exasperated remark.
"Lord Dan Lei, with an expert of the Celestial Realm like Lord Kojiro Sasaki by your side, why would you need to learn the Breathing Technique from me?"
Before you continue