The otaku died of a terminal illness and took over the body of Kokushibo from the Demon Slayer world.

In order to survive and make up for some of the regrets he had when watching the anime, he decided to become Kokushibo and live in this world...

Having transmigrated into the world of Demon Slayer, Mugae became Muzan Kibutsuji's adopted son and became Kokushibo's apprentice to learn Moon Breathing. The young prince Mugae declared that with this identity, he could roam freely throughout the entire demon world!

Muzan Kibutsuji: He's such a filial son, I'm dying of filial piety. I never want to kill his father with Tamayo.

Domo: I treat Wuya like a young master. The young master always wants to treat me to wisteria flower tea, and he also likes to take me out to bask in the sun. He's so considerate!

Jade Pot: Young Master Wuya is a hypocrite. He says my pot is asymmetrical, but secretly he sells it for money!

Naruto: With Young Master Wuya's praise and recognition, my flute playing skills are getting better and better!

Lin Yan traveled through time and space in the blink of an eye. He traveled to the world of Demon Slayer, to the body of a dying beggar. The wind was freezing cold, and Lin Yan had no strength at all. He could only huddle in a corner, feeling the vitality in his body gradually disappearing in despair. As a traveler, he even had the golden finger [a system that can make you stronger by eating], but he had no chance to use it. After all, the reason why he fell into such a situation was because he had nothing to eat. At this moment, a pair of slightly immature hands full of wounds pulled Lin Yan up.

A boy named Uchiha Mei lost his parents to demons when he was ten years old. He met the Flame Pillar, Rengoku Makijuro, and became his disciple, possessing extraordinary talent. He formed a bond with the Flower Pillar, Kocho Kanae, becoming Tanjiro's teacher. He arrived in time to fight Child Demon when Kanae was attacked. He instinctively killed Child Demon, but Kanae was seriously injured. To ensure Kanae's safety, he inadvertently allowed Child Demon to escape. He later became the Fiend Pillar.

A young man from the modern era travels to the Demon Slayer world and becomes the descendant of Tsugakuin Yoriichi – Tsugakuin Najo. The protagonist is born with markings and natural transparency. There are two female protagonists (guess who they are): Muzan: "Don't come over here!" Kokushibo: "Come on, you will finish Yoriichi's unfinished duel!" Sango: "The ultimate battle!" (Slightly altered plot) (This book is not a cool novel; just having markings and transparency doesn't mean you can easily kill an Upper Rank! It's a coming-of-age novel.)

(Pseudo-invincible + female lead Shinobu Kocho + system runs away at the start) Shimotsuki Mirai transmigrated to the present day and has spent her childhood wandering around the forges of the sword-forging village, the clanging of hammers the lullaby of her life. The blacksmiths always said this child's eyes were too still, as still as a quenched blade, unaware that the vermilion burn marks on his palms, shrouded in years of wear, concealed an astonishing power no less than that of a Nichirin Blade. When he first met Shinobu Kocho, he only felt a stinging pain in his eyes. Before seeing the girl, all his information about her came from the precious little black box he couldn't bear to part with in his previous life, but now, the person from his dreams stood before him, more vivid than any description. The girl blushed, staring at the light dancing on his fingertips, asking if he was a deity descended to earth. Kanae leaned against the door, chuckling softly, "Such a wondrous boy is hidden in the sword-forging village." Looking into the clarity in the girl's eyes, Shimotsuki Mirai suddenly wanted the sword in his hand to protect that light a little longer, just a little longer...

Since he regained consciousness, Yang Quan has been staying in a dilapidated house. Having lost his memory, he didn't know where to go, so he stayed here.

One day

A butterfly-like girl suddenly appeared in the soft moonlight, and Yangquan learned from her that he had become a ghost.

The girl had a gentle smile on her face, but it didn't show in her eyes. She said she wanted to get along well with the ghost, but she stabbed Yangquan with her light knife.

What Yang Quan never expected was that in the near future, a girl named Shinobu Kocho would hold his face and look at him straight.

"Mr. Yangquan, please stay with me forever!"

..........

It was not until a long time later that Yangquan heard his own answer.

"good"

"Hey? System! What do you mean Nohara Shinnosuke is a Pillar? What do you mean Uchiha Sasuke is a Pillar? What do you mean the Pillar Men and Hashirama are Pillars? Tailed Beast Jinchuriki? Josuke Higashikata can do that too?!" Lu Li unexpectedly transmigrated into "Demon Slayer" and awakened the Demon Slayer "Pillar" Summoning System! Every three days, Lu Li can randomly draw a "Pillar" and gain all of their abilities. Just as he was excitedly preparing to open the system and use the Pillars' abilities to fight Muzan, Lu Li discovered that the "Pillar" drawn by the system seemed a little different from what he expected. "Hey! System! I can tolerate the previous ones! But system, what the hell is this Optimus Pillar you summoned? Kibutsuji Muzan, huh?! Kokushibo, huh?! Tell my luck!" ...Tentative protagonist's alternate worlds: "Demon Slayer," "Fate/Zero," ...

Su Chen traveled through Demon Slayer's Spider Mountain and almost got killed as he landed.

At the critical moment, he awakens the golden finger and has an incredible understanding.

In the end, he was injured and rescued by Shinobu Kocho and became a member of the "Butterfly House".

Su Chen goes out with Shinobu Kocho to rescue people during the day, and secretly kills ghosts at night to make money to support the girls in the Butterfly House.

While walking, constantly use the golden finger to observe and learn.

[You observed Shinobu Kocho's healing process and gained something from it. You created your own skill: Supreme Poisonous Healing!]

[You observed Kanao's sword training and suddenly an idea struck you, revealing a unique sword technique. A thought blossomed!]

You spied on the former Sound Pillar's thunder cry, gathering mosquitoes into thunder. Deeply impressed, you modified it slightly and developed the Lightning Release - Chidori Style!

From then on, Butterfly House had a famous and evil male doctor.

When everyone asked Su Chen why he worked so hard, Su Chen's thoughts were very simple.

"Why kill ghosts? Of course, it's to keep the flowers in the Butterfly House working well and feeding them!"