Fox Demon: Heaven rewards diligence; I will eventually achieve divine mastery of martial arts.

Of course, why did Lin Yu say it wasn't important?

This is also for this reason. After all, the instincts of the body's cells are too powerful, so in some research, there is no need for something like Muzan Kibutsuji's soul.

"I will list some possibilities that I have thought of, and you can try them out first."

Lin Yu analyzed.

While Lin Yu's soul was traveling in the extraterrestrial demon world, he pondered many speculations about Muzan Kibutsuji's body.

Tu Shan Rongrong nodded.

Lin Yu paused for a moment and then said:

"There's no need to rush this matter. Take it slow. Perhaps the experiences of other spirits in other worlds can provide us with some reference. So take your time. More importantly, take care of your health. You haven't been sleeping much lately, have you?"

Hearing Lin Yu's concern, Tu Shan Rongrong, whose expression had remained calm, blushed slightly and shook her head.

"I'm not tired. Besides, you've been working hard to explore the extraterrestrial demons for so many days, so I should work hard too."

"Haha, should I praise you then?"

Lin Yu patted Tu Shan Rongrong's head, and Tu Shan Rongrong's face showed a look of enjoyment.

"But while we should work hard, we need to conserve our energy for things that can't be rushed."

Lin Yu spoke, glancing at the bed and then at Muzan Kibutsuji. After a moment's thought, he whispered a few words in Tu Shan Rongrong's ear, and Tu Shan Rongrong's cheeks immediately turned red at a visible speed.

However, he nodded in the end.

After activating the protective measures in the laboratory, she and Lin Yu walked out of the place that had been converted into a research lab.

…………

Kibutsuji Muzan opened his eyes.

He felt as if he had a very long dream.

He dreamt that he was so frightened by an incredibly terrifying being that he fainted.

All I remember is that devastating punch that was aimed at him as he charged towards me, and then...

Muzan Kibutsuji shook his head. He couldn't remember anything at all now, but he could only recall one feeling: a deep sense of powerlessness.

It felt as if I had been run over by some heavy object time and time again.

Muzan Kibutsuji was somewhat speechless, unsure why he had such a misconception, especially after he became a demon...

Thinking of this, Muzan Kibutsuji glanced around and was immediately bewildered, because he saw that he was now inside a huge transparent glass dome.

Outside, there were only some strange and unusual devices.

"In the end what happened?"

Muzan Kibutsuji was somewhat surprised, but this was quickly followed by anger, because he had been the progenitor of demons for so many years, yet he had never been imprisoned.

He immediately changed the shape of his arm, twisting it into a sharp spike, and stabbed at the transparent glass dome in front of him.

To his utter surprise, his attack, which could easily crack the ground, made no sound at all on the transparent shield.

There wasn't even a single mark left on it.

After the initial surprise came an even fiercer, burning anger.

His body evolved countless tentacles, which fell towards the transparent dome.

This high frequency of attacks finally made Muzan Kibutsuji see some things clearly.

For example, when his tentacles landed on the glass dome, an invisible ripple spread out.

So what appears to be an attack on the transparent glass dome is actually something else blocking his way.

Muzan Kibutsuji calmed down and extended his tentacles to spread around him, trying to see if there was any empty space.

But in the end he failed. He could only choose one place and attack it frantically, trying to break through the barrier and see if he could escape from this strange and powerful cage.

However, Muzan Kibutsuji had always found that the barrier remained completely still, and that every time his attack landed on that invisible barrier, the ripples it created were always about the same size.

He was somewhat desperate, but he still wanted to leave, so he stopped and began to think.

Just then, a voice came from a great distance.

"you're awake."

Muzan Kibutsuji raised his head and suddenly noticed a strange human in front of him.

While it's described as human, that's not entirely accurate, given its pointed ears and tail, which suggest it's not human.

"fox?"

Kibutsuji Muzan was somewhat puzzled.

“It seems there’s nothing wrong with your perception,” the beautiful woman, who resembled a fox, said, taking out a metal-like object and tracing it across. “Now, I’ll ask you a few questions…”

Before he could finish speaking, he was interrupted by Muzan Kibutsuji:

"Who are you? Why are you trapping me here? I warn you, release me immediately!"

Anger flashed in Muzan Kibutsuji's eyes.

However, the other party sighed and said:

"As expected, even without the influence of the extraterrestrial demons, it's still this volatile?"

Tu Shan Rongrong shook her head. Two or three days had passed since Lin Yu brought Kibutsuji Muzan back to the Fox Spirit World. Although she had just returned from her tender moments with Lin Yu to her research, she quickly got back into the swing of things.

So she started writing "irritable" as a comment on the personality test results of the test subjects.

"Woman, are you even listening to me?"

When Muzan Kibutsuji saw that Tushan Rongrong completely ignored him and even disregarded his behavior, he became furious and waved his countless tentacles. Just then, another voice rang out.

"Oh? You're already so energetic after just waking up."

Upon hearing this voice, Tu Shan Rongrong's face immediately showed a faint expression of happiness, and she turned her head and said:

"Brother Lin Yu, you're here."

At that moment, Lin Yu walked over from the entrance of the research room.

"It's you!"

The moment Muzan Kibutsuji saw Lin Yu, it was as if a thunderbolt struck his mind, and he suddenly remembered many things from the past.

She even remembered why he had fallen into a coma—it was because of that horrific attack.

Upon realizing this, Muzan Kibutsuji's face immediately showed a look of panic as he stared at Lin Yu in terror.

"You...you are who you are!"

"Brother Lin Yu, it seems he's quite afraid of you."

Tu Shan Rongrong looked at Kibutsuji Muzan with great interest. Kibutsuji Muzan's face now was a stark contrast to what it had just looked like, making people laugh.

"Well, after all, I was the one who defeated him."

Lin Yu nodded. He hadn't gone into detail about the final battle, such as the existence of even more powerful extraterrestrial demons spying on the Demon Slayer world.

After all, the women are still too weak, and talking about many things would only bring no benefit.

"However, this is also his own fault. After all, he has experience using other people as test subjects, so he should be prepared to put himself on the test bench as well."

Tu Shan Rongrong said coldly.

Although she doesn't usually show her emotions, she is actually very clear about her hatred. She naturally hates people like Kibutsuji Muzan who kill their benefactors.

"Test bench?"

Upon hearing these words, Kibutsuji Muzan was stunned and looked at the two people in front of him in disbelief.

Am I being used as a guinea pig?

Kibutsuji Muzan was shocked.

How can this be?

I am clearly the progenitor of evil spirits, yet I am the one who gets to be the subject of others' experiments.

But no matter how much he disbelieved it, the facts were right in front of him: with Lin Yu's strength, he was just meat on the chopping block.

Just like the humans he casually discarded after completing his experiments, they were powerless to resist.

Lin Yu snorted coldly at the other party's appearance:

"Muzan Kibutsuji, do you think death is the most terrifying thing in the world? I'll tell you what the most terrifying thing in the world really is."

Having spent two years with Tanjiro Kamado, Lin Yu naturally disliked Muzan Kibutsuji, feeling that letting him die so easily was too lenient.

So he could have erased the memories stored in Muzan Kibutsuji's soul, but he didn't.

The purpose was to make Muzan Kibutsuji experience the pain that the others had felt back then.

"No, you can't do that! I am the progenitor of evil spirits! I can give you my blood and grant you eternal life!"

Kibutsuji Muzan's fear reached its peak, and he immediately broke down.

Lin Yu ignored the other party and spoke directly to Tu Shan Rongrong:

"Let's begin the experiment. He's still in good spirits now. We can inject him with blood when he's about to pass out."