A wave of dizziness suddenly washed over Kenshi, his vision blurring. His head started swaying as he flopped back on the pillow.

"Kenshi? Are you okay?" Shinobu's brows creased with concern as she reached out to steady him.

He opened his mouth to respond but felt his consciousness rapidly slipping away. Darkness closed in around the edges of his sight as an overwhelming drowsiness pulled him under.

The last thing he registered was the worried look on Shinobu's face before everything faded to black.

Shinobu watched apprehensively as Kenshi's eyes rolled back, and his body went completely limp. For a split second, panic gripped her - had that damned spider venom resurfaced again?

But then she noticed his steady breathing, and after observing for a few seconds, she realized he had simply fallen into an ordinary sleep. She let out a soft sigh of relief.

Looking at the dark circles under her own eyes, it was easy to identify that she hadn't gotten much sleep in a long time. She rested her head on the bed and fell asleep again.

As the two slept, Kenshi found his consciousness pulled into a vast expanse of nothingness. He opened his eyes but saw only a red flame glowing in the vast... nothingness. No light, no shapes, or features of any kind. Just an endless void of infinite darkness surrounding him, other than the red flame a few meters away from him. He could see nothing else.

"Uh... where the hell am I?" His words seemed to get swallowed up by the darkness.

[System integration sequence initiated.]

Kenshi jumped at the sudden mechanical voice echoing all around him. "What's happening?"

In response, a futuristic transparent blue screen materialized out of nowhere in front of him. It was a holographic display with lights flickering across it's surface.

[Apologies for the disorientation, host. We are within your mindscape. You have met the right condition to fully integrate with the system. Host needs to wait a few seconds as I complete the assimilation process.]

That same robotic voice spoke calmly.

[Please remain still while I reconfigure your physiological and mental condition.]

Before Kenshi could say anything, a whirlwind of glowing blue particles started spiraling around his body. He was tense for a moment but found himself completely immobilized by some unseen force as the luminescent lights enveloped him.

Searing energy flooded through his veins like liquid fire as the mysterious process took hold.

Outside, while Shinobu slept soundly, changes started taking place in Kenshi's body.

Large sweat droplets appeared on his body as his muscles burned intensely. Inside the mindspace, Kenshi fell down and started roaring with pain, feeling like his muscles were being shredded apart at the cellular level and forcibly remolded. A deafening roar filled his ears, drowning out all other senses until he thought his head might explode.

Just when he felt he couldn't endure any more, the torrent of agonizing sensations reached a sudden stop and abruptly cut off. Kenshi crumpled to one knee while gasping for air. But he felt... somehow different now, like his very being had been recalibrated down to its core.

His mind had felt an incredible amount of fatigue after being cured from the poison, yet now, he was feeling as usual, actually better than usual, like his soul and mind had suddenly become calm.

[Integration complete.] The robotic voice sounded.

[You may access the system's various functions now.]

Kenshi looked up at the holographic screen, only to be bombarded by a flurry of rapidly changing displays, menus, and option trees flickering across its surface. Too much information to parse all at once.

[Allow me to explain your new abilities systematically.]

The system seemed to sense his confusion and overwhelmed state.

[My prime function is to issue you progressively challenging missions. Successfully complete them, and you'll get rewards, points, and future skills.]

A new window materialized, showing an expansive skill tree with various nodes and paths connected in an intricate web.

[This is the Skill Tree interface. You can spend points to access new techniques, abilities, and more.]

Another display flickered into view, this one showing a series of complex, overlapping symbols and glyphs.

[The Ability Synthesis matrix lets you combine different skills into powerful hybrid techniques tailored for different situations. Mastering this will prove crucial against superior foes.]

The windows kept cycling through in quick succession -

[Simulation Mode: The system now has a simulation mode that allows the host to enter his mindspace to train and practice his abilities in a virtual environment, allowing him to push his limits without real-world consequences. However, other than mentally training and discovering your skills, it does not help with anything related to physical abilities.]

[Analytical Capabilities: The system has enhanced the host's body and mind, so that the host can have analytical abilities, allowing the host to study and comprehend complex techniques and strategies at an accelerated rate.]

[Better mission performance earns system points to further buy or upgrade the existing skills.]

The system's voice paused, seemingly awaiting acknowledgment. Kenshi slowly exhaled, struggling and also a little excited about everything that was happening.

"Huff... all this seems interesting, but are these skills enough to rival my enemy's strength?" He asked.

[If the host stops whining about the training and starts training seriously, with the system's current skills and abilities, it's guaranteed that the host will become a Hashira in less than a month.] The system responded flatly.

Without saying anything back to the system like he does usually, Kenshi nodded slowly.

"I'm guessing these missions have to do with... Edward. That anomaly you mentioned before."

[Correct. Neutralizing Edward and his plans is now the top priority objective.]

The system spoke with an ominous undercurrent laced in its robotic tones.

The infinite darkness surrounding them seemed to intensify as the atmosphere took a more serious edge.

[The system would like to inform the host that Edward stands apart from any threat you've previously encountered. His very existence violates the natural laws and boundaries governing this reality. Defeating him will demand you surpass all conventional limits.]

That arrogant child-like figure he had seen last time had already radiated a sense of power and malice he could scarcely comprehend. If the system's warnings rang true...

His expression hardened with determination as he clenched his fists. "Alright then. Tell me what I need to do."

[First, focus on integrating with and mastering the system's various functions.] The system instructed. 

[Take full advantage of the simulation and training modules and do not underestimate the challenges ahead.]

Hearing this, Kenshi nodded. He knew if he didn't become the strongest, only death awaited him as he progressed further.

"Everything is alright. But, what is this red flame in my mindspace? Is this supposed to be in everyone's mindspace?"

[I was waiting for the host to ask that question. The mindspace is completely empty, as for this flame, it was planted by Edward when he talked to the host last time.]

"W-what! It was planted by Edward? What exactly is this? Will it cause harm to me? Forget all that, how can I eradicate this thing from my mindspace?" Kenshi was taken aback to know what it was. And if it was planted by Edward, surely it would cause harm to him in some way, right?

[The host need not worry for now. If the host wants to know about this flame, you need to understand what a mindspace is. The mindspace is a place that exists within a person. Many normal people have thought it was illusory or false, but some people tried to access it, and with different methods, only a few succeeded. In the mindspace, people can strengthen their mental fortitude, train, or even build their own world if they are strong enough.]

[However, its true potential has been discovered later, that many things can be done through this mindspace. For example, this flame is called a mind flame. People who become experts in using the mindspace can create a flame called a mind flame, and after nurturing it for many years, they will have access to a limited number of flames called branch flames originated from the mind flame. The person who had the branch flames can plant these flames into another person if they come into contact with said person's mindspace.]

[This flame will grow in that person and make them a puppet for the person who planted the flame. Since in this era, not many people know about the mindspace, they won't even discover that a branch flame was planted in their mindspace.]

Kenshi just stood stunned at the information. There was such a thing in the Demon Slayer world? Why had he never heard about it?

"Then why did you tell me not to worry about the flame?" He asked, remembering what the system had said.

[Mindflames and branch flames have many different quality levels. A person with the highest quality mindflame can even bring it into the real world and use it in battles, and what the host has was the lowest level, which was called an infant branch flame. Even if it stayed inside the host for a thousand years, it won't cause any harm to the host in any way. That being said, eradicating the flame is not an easy process, but the system suggests the host not do it since the host can turn it into an opportunity for himself. Other than this, no further details will be given to the host about the mindspace.]

"Hhhhh, so Edward now has this weird flame that can turn people into his puppets. Excellent. I seriously regret cursing at the unbeatable video game bosses because beating them seems so easy compared to this bastard now." After that, he tried to ask the system a few questions, like a way to remove the flame if something unnecessary happens, but the system only said, [Figure it out yourself.]

So he ended his questions. He tried to mess with the branch flame that was beside him, but it seemed more like an illusion than a real flame, so he stopped. After reviewing all the abilities he had now and all the information the system had given him a few times -

He closed his eyes, steadying his breathing as his mind raced. This system... it was his key to finally taking an active role in shaping events instead of being railroaded by the plot.

Most importantly, it represented his best chance at overcoming that ominous enemy and the many upcoming enemies that he was going to face.

A fierce determination blazed in Kenshi's eyes as his consciousness slowly returned to the real world...

---

Some time later, Shinobu woke up, her body stiff and sore from the awkward position she had fallen asleep at Kenshi's side. Rubbing the lingering grogginess from her eyes, she glanced over to check on her pupil.

Relief washed over her as she noted his chest rising and falling steadily with the motions of peaceful slumber. Gently, Shinobu reached out and laid the back of her hand across his forehead, checking for any signs of fever or lingering venom effects. She found none, but she saw sweat marks on his pillow.

"It's not hot in the room. Why is he sweating? Maybe I should open the windows." A small smile appeared at the corners of her lips.

Carefully, so as not to disturb Kenshi's rest, Shinobu stood up and stretched her thin frame, then walked towards the window and opened the doors, allowing the cool air to flow inside. The incidents that were happening lately had caused a lot of panic and fear in her that she would again lose someone close to her.

Giyu, her fellow Hashira, struck down and gravely wounded. And the poor boy named Tanjiro's younger sister, mercilessly abducted. And of course, Kenshi, her own student, had nearly died at the hands of that spider demon. And then Kanao-

Her jaw clenched as images from that battle against the demon flashed through Shinobu's mind.

Losing him would have been utterly devastating, like it was with...

Just as she was thinking this, she suddenly heard the rustling of the bedsheets, which made her look back.

She saw her student had opened his eyes, but when she saw his face, her jaw dropped wide, and her eyes became big.

Kenshi, her student who had black hair, now had purple hair, and it seemed his height had also improved, and many changes had occurred in his face and body that she was contemplating if her student was possessed or something. Wasn't he normal just a moment ago?