Tanjiro's Past in the New World.

Tanjiro entered the door made of green light with old Juki. As he entered, Tanjiro found himself in a completely different dimension.

Tanjiro could feel the purity of air was several times better than the outside world. The natural mana in this place was very dense. Just standing in this place, Tanjiro felt his 'Mana Sense' skill improve.

The skies looked blue like in the outside world, but it felt very different for Tanjiro. The Sun in the sky also gave Tanjiro a weird feeling. This place, as far as he can see, were full of trees, like a big forest. He could also feel various life forms in the forest, due to his newly acquired skill 'Mana Sense'.

"Young master, this place is as big as a moderately large island. The Sun in this dimension was artificially created by predecessors of Kamado clan. There is also an artificially created moon. They were created so the life could be properly maintained in this hidden dimension." Juki said in a casual tone.

"…"

Even though he has experienced many supernatural aspects in his previous life as a demon slayer, what he just experienced tops it all.

Katakiri Juki looked at Tanjiro, who had a speechless expression, chuckled softly and said,

"Young master, this is a separate dimension created by the predecessors of Kamado clan in the distant past. Only those with the blood of Kamado can enter this dimension with the use of the divine spell: Hidden Gate. In this world, the only ones who can ignore this condition and enter this dimension are the two Dragon Gods. Though, they wouldn't really bother with this dimension, since there is nothing here that can get the attention of those all-powerful beings."

"Dragon Gods? Ah… I'm starting to understand why Alficius-san said that this world has many powerful beings that can make demons look like nothing." Tanjiro thought with a bitter smile. Then, he noticed something off about Juki's words.

"Then… why are you able to enter this place then, Juki-jiisan? Are you from some sort of branch family of Kamado clan?" Tanjiro asked confusedly.

"Haha, it's nothing like that, Young master." Juki laughed, then he took out a green talisman with the word 'Gate' written on it.

"This talisman was given to me by your grandfather. It's because of this talisman that I'm able to use the divine spell to enter this dimension." Juki explained, to which Tanjiro nodded in understanding.

Looking at Tanjiro nodding his head, Juki smiled slightly.

"Young master, do you remember how your parents perished?" Juki suddenly asked with a serious expression.

"… It's from a car accident, right?" Tanjiro replied in an unsure tone.

At least, that's what he remembered.

"The car accident was just a cover up to hide the real cause of your parents' death."

"!?"

"An unknown humanoid monster with the strength of a low-class supernatural being appeared out of nowhere, a few months prior to your birth. It tried to attack your mother, but was intercepted by your father and defeated. But it managed to get away. At that time, we weren't sure of its motives in attacking your mother."

"That's…. But why?" Tanjiro asked. But he didn't get an answer, as Juki continued on with his story.

"The monster attacked again and fought with your father. Only this time, it was significantly stronger than the previous encounter. It had actually reach the level of a high-class supernatural being in just a month. But your father was able to make it retreat."

"Juki-jiisan… I'm completely lost here."

"Ah.. you see, there are various factions of supernatural beings such as devils, fallen angels, vampires, youkais, pantheons of the gods of different mythologies, the heaven which is maintained by the God of Bible and a few others. Anyway, the power levels of the supernatural beings are commonly classified as low-class, mid-class, high-class, ultimate-class and faction leader level. The faction leader level is the pinnacle stage of the ultimate-class." Juki said.

"… I see…" Tanjiro was speechless.

"Let's continue. Your father let your grandfather know of the unknown monster, as he felt that he wouldn't be able to handle it the next time it returns. Soon you were born, young master. The child born with the 'Evil Slayer Mark of Sun'. Your birth was the cause of celebration in the clan."

"…"

Seeing that Tanjiro had a puzzled look on his face, Juki further explained.

"Other than you, the only one who possessed the 'Evil Slayer Mark of Sun' was the first Evil Slayer. Just his name alone is capable of striking fear in the majority of the factions of supernaturals."

"I don't know why… but this seems quite familiar to the situation of the first user of 'Breath of Sun' Yoroichi Tsugukuni." Tanjiro thought with a speechless expression. He had a feeling that, Alficius had created this background for him, instead of it being natural.

"But, good times didn't last long. A month after you were born, the monster appeared again. I, myself was there with your grandfather and father. But when we faced the monster, we immediately understood that we couldn't win. The monster had attained power rivaling that of the faction leaders or even higher. We were soon overwhelmed. And because of our carelessness, the monster struck at your mother and you, or rather, it attacked you, to be precise." Juki said.

"Then that means…" Tanjiro was shocked, yet confused.

"Yes, the monster's target has been you from the start. We presume that it was afraid of your existence. It was then the tragedy began. The assembled combatant members of the clan were killed by the monster when they protected you and your mother. In the end, even your mother died while protecting you. Your father and grandfather also perished under the monster. I was also severely injured with the infant you in my arms."

"…" Tanjiro couldn't understand why the monster wanted to kill him so much. He felt angry at this display of unreasonable aggression. This kind of obsession to kill him was on the level of Kibutsuji Muzan.

"But it didn't end there." Juki said as a smile formed on his face.

"Huh?"

"Immense luck shone on you at that moment, young master. Because, one of the two Dragon Gods, The Ouroboros Dragon came down and declared the unknown monster as 'Harmful Outsider'. Then the Ouroboros Dragon effortlessly annihilated the monster. Nothing remained of it. When I watched the monster being erased so easily, it all felt so anti-climactic. Regardless, the Ouroboros Dragon may have done it on a whim, but she indirectly saved your life. Even now, I'm very grateful to her."

"…"

"System, that monster is.." Tanjiro asked in his mind.

[It is as you guessed, Tanjiro. That monster was a being from different dimension. It was probably sent to this dimension to eliminate you by one of 'True Creator' Alficius's enemies. Considering your potential rank and the system you received, it's quite normal that they think of eliminating you before you become a problem for them.]

"Alficius-san, the mission you gave me doesn't seem like an easy one…" Tanjiro thought as he sighed.

…

Tanjiro kept on listening to Juki. But when the old caretaker said about Evil Slayers, which quite surprised Tanjiro, as it was very different from what he envisioned.

The Evil Slayers were not exactly the same as the Demon Slayers from his past life.

The Evil Slayers of this world used techniques known as Divine Spells to fight against Demons in the historic period. The most basic, yet, important spell of the Evil Slayers was called "Sanctification". Only by mastering this Divine Spell can one be called an Evil Slayer.

But, despite being a basic spell, this spell was in the study of souls, which was quite a complicated field of study. Hence there weren't many Evil Slayers, even in the historic times.

At present, after the incident with the unknown monster, the only remaining Evil Slayer is Katakiri Juki, as most of the surviving members of Kamado clan were normal people.

Hence, Juki intends on training Tanjiro on being a Evil Slayer as he doesn't want the legacy to be lost.

Though, Tanjiro felt all this to be meaningless. Because almost no man-eating demon exists in this era. So he saw no point in learning all the spells that used to deal with specific demons.

But Tanjiro didn't voice any objection despite his thoughts, as he felt that this is also one of his responsibilities in this new life.

A man must never run from his responsibilities. This is something his father and teachers taught him in his previous life.

…

After half an hour.

Katakiri Juki and Tanjiro returned to the Kamado residence from the hidden dimension.

"Young master, go freshen up a bit, then we'll go out for a walk." Old Juki said in a soft tone.

"A walk? Juki-jiisan, after everything you told me, my state of mind is quite complicated now. I'm not in the mood for a walk." Tanjiro said, feeling tired.

"Don't be like that now, young master. Don't be upset in a day like this. It's your birthday after all. Even though I revealed what happened in the past, it's still past in the end. You just need to live in the present while looking forward to the future. I just said about your past for obligation purpose. You don't have to pay great heed to it." Juki said in a helpless tone.

"Then why did you even bother saying all that to me?"

"It's so that you don't forget that you're living with the sacrifice of your parents, grandfather and many clan members. So remember, it is your responsibility to live a fulfilling life for their sake as well. Just make sure to train and be strong enough to protect yourself, so that their sacrifice wasn't meaningless." Juki said in a firm voice.

As he heard Juki's words, Tanjiro felt so much better.

"Yes." Tanjiro nodded.

"Mn, Good. Now, go get ready." Juki said with a smile as he walked away.

Tanjiro looked at Juki's back and thought..

"Juki-jiisan kind of remind me of Rengoku-san."