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{This is my first time writing a story. I never wrote one for someone else to read. I took inspiration from many different stories. I'm not claiming all the ideas i will use in this story as mine, maybe they have already been used in a much better way. Conclusion, I'm a novice. I'm not claiming that you will like this story. Hope you give constructive criticism.}
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{Oh and English is not my first language. You may find a few errors but I will try to convey the story in a way that most people can understand, atleast I hope so.}
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The Demon Slayer volume is complete.
Muzan will directly move to his next world from here.
Below is the System's evaluation and rewards for Muzan.
Previous condition: His soul was saturated with accumulated resentment from centuries of devouring humans and absorbing demons. This is according to my own setting.
(Seeing how the soul was a recurring theme in Demon Slayer, I thought of applying it more thoroughly.)
That residue acted as metaphysical interference, which, in short, acted like cuffs on him.
His growth was dulled.
Yoriichi's wounds were not simple injuries but conceptual obstructions embedded in internal channels, restricting output. This doesn't mean Yoriichi was casually using conceptual-level attacks, but more like it was fate and destiny helping him.
It wouldn't be a lie to say Yoriichi truly came to stop Muzan, and while Muzan did manage to escape, he was permanently crippled. His power was capped.
The point is that negative karma and the accumulated resentment and everything, these are not fictional things. These are very real, and even the world acts in order to remove such filth.
"The hero being born to end the demon king's reign" cliché is not just a stupid cliché after all.
Anyway!
Current condition: After facing all his accumulated resentment, negativity, and the projections left by those devoured by him, all spiritual obstructions are now removed. Resentment has been cleared. The metaphysical scarring has been erased.
Soul integrity has increased approximately one hundredfold in density and stability. This is not an exaggeration. Even just a small part of the essence left by those images in the confrontation has been used by the system to reinforce Muzan's soul.
This does not mean he's a saint or he's become a better man. It's simply structurally reinforced; his personality won't be affected.
With the soul's foundation stabilized, the body followed.
Physical form has been fully optimized. No lingering scar tissue. No dormant spiritual burns. Regeneration now operates cleanly and efficiently. Cellular control is precise. Full operational capacity restored for the first time in centuries.
And yes! This also means that the Muzan everyone saw in canon was already very weak. This is not canon; this is my addition to my own story.
Because I refuse to believe how dumb and weak the guy was after a whole thousand years of prep time.
System classification: Physically Immortal.
Flesh destruction is irrelevant. Total cellular pulverization results in reformation. No aging. No decay. No natural stagnation. Conventional attacks are ineffective.
Remaining vulnerability category: Conceptual interference. As in, conceptual attacks still do damage and can kill him. Soul attacks can damage his soul, but now normal soul attacks wouldn't be able to do that.
Imagine you had a soul-cutting knife; now that thing isn't effective enough on Muzan. Now you will have to pull out not a gun, but a rifle!
System function: Multiversal traversal. No fixed world, timeline, or dimension. Relocation available at will.
Primary strategic advantage: Freedom of engagement.
Recent system evaluation granted structural enhancement rather than external artifacts.
Now, let's talk about something else. This is also a part of the system's reward for him, but it's more of something I should explain first.
Blood Demon Arts.
Now the concept of Blood Demon Arts is cool, but the explanation is vague. Like how they manifest, we know when a demon eats enough people or has enough energy or has enough emotions (Nezuko?), it can manifest its Blood Demon Art.
But how do they work?
Well, from what I imagine, Blood Demon Arts are manifestations of vitality or life force, circulated through specialized internal channels unique to demonic physiology.
Something like Ki or magic, you know, like mana veins or magic circuits?
Output depends on structural design and the volume of life force available.
So the primary resource is the accumulated life force.
That also kind of gets into why demons can only eat humans.
As the evolved form of humans, human life force has the closest compatibility to them.
Blood Demon Arts require life force and compatible internal frameworks. Conflicting architectures create instability; unlimited stacking is unsustainable.
And that's where the system's reward comes in!
System allowance: Three Blood Demon Art structures. And these structures will directly be fused with Muzan. For now, in short, Muzan now has three additional Blood Demon Arts.
Now, let's talk about his reserves, as in, his life force.
He consumed, absorbed, or dismantled over 600,000 humans and over 17,000 demons.
Believe me or not, that's a LOT!
For example, as a conservative estimate:
If each human equals one year of remaining vitality, the total exceeds 600,000 years. Including demons, if each demon equals one year as well, the reserve surpasses 617,000 years, and that's only because we're being extremely conservative. However, if we, average it, because no-one would really believe Muzan was eating Old people who were only 1 or 2 years away from their deaths right? So we hit it higher instead!
Then the estimate should be:
Average 10 years per human yields roughly 6,000,000 years.
Demons at at least 50 years each add approximately 850,000 years.
Estimated reserve: over 6,850,000 years of vitality.
Fuel was never the limitation for dear Muzan; circulation interference was. With channels cleared, full output is now possible.
With his repaired and reinforced channels and multi-million-year reserves, manifestation scale exceeds previous limits by orders of magnitude. Regeneration speed increased. Energy output stabilized. No stagnation feedback. No internal drag.
Operational state:
Soul: Reinforced, ~100× stability increase.
Body: Fully optimized.
Immortality: Physically Absolute, except against conceptual attacks.
Life-force reserve: 6,850,000+ years equivalent.
Blood Demon Arts: Three compatible frameworks sustained at extreme output.
Traversal: Active and unrestricted.
Karmic interference: Eliminated.
Status: Unshackled, fully optimized, multiverse-ready.