It's a very rare gu and where would he have found it? Since simply being born that strong is known to be a thing that's a simpler default explanation.
"What is there to be suspicious about? There are always people who are born with strange talents. Either super strength, or super smart, actually Fang Yuan's strength isn't that scary, think about that guy." The speaking Gu Master indicated at the standing Chi Shan.
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Eastern · Gu Zhen Ren
It's better than average but not exceptional. Potentially a good valuable member of the clan that could become an elder if allowed to live long enough, but not an A rank genius that can singlehandedly shift the balance of power in the cman's favor.
Back then, the family all thought well of him, thinking he was an A grade. But during the awakening ceremony, they tested that his talent was only B grade.
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Eastern · Gu Zhen Ren
Well there's a point where extorting might not be possible anymore, so while not an actually urgent problem, it is not sustainable long term. Also don't bother too hard nitpicking the author's maths, it turns into a joke that he isn't good at it (to the point where the author himself make fun of it in a later scene).
On hand at the moment, he had several hundred primeval stones, but it was not enough to sustain such an expenditure in the long run.
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Eastern · Gu Zhen Ren
Because it's just the early stage. His talent will slow him down more and more without extreme methods and the spending of significant more resources to compensate. Even more significant, his lack of talent cap his potential. A C grade would be lucky to eventually get to rank 3, but what the clan leader need is a rank 4 potential successor, and that's basically not happening without a way to increase talent, which the clan does not have.
"I analyzed Mo Bei and Chi Cheng's personality for Fang Zheng, but he did not notice my intention, instead asking about Fang Yuan's situation. It seems that he has great trauma regarding Fang Yuan, but he is also at his rebellious stage. He wants to beat Fang Yuan, that's understandable. Sigh, if only Fang Zheng had Fang Yuan's intelligence, I've seen many youngsters these years, but when it comes to political wits, Fang Yuan tops them all. It is a pity he only has C grade talent."]
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Eastern · Gu Zhen Ren
They are a way to stabilize the aperture by imitating the outside world. The details should be in a chapter before the crazed demon cave arc.
The sovereign immortal aperture's time flow was very different from the five regions' outside world. All kinds of dao veins were constructed rapidly, metal path, light path, dark path, poison path, rule path, enslavement path, transformation path…
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Eastern · Gu Zhen Ren
I imagine him being like those animals that kill and eat their partner. It does seems to be his solution to everything after all.
All the ten venerables had partners in their lives, only the number was different.
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Eastern · Gu Zhen Ren
Spectral soul did use him as a pawn secretely, but did not directly control him, so there's nothing weird about longevity heaven also making use of him.
Ma Hong Yun had the power of Fortune Rivalling Heaven, he seemed to be someone who started from a humble origin, he was able to unite many lone and demonic immortals as a result. But he was in fact Longevity Heaven's chess piece, an arrangement of Giant Sun Immortal Venerable.
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Eastern · Gu Zhen Ren
It was originally the monk's vital gu, which can't easily be replaced and he had it presumably to rank 5 or at least 4. Lacking sufficient food but presumably not to the extend of starving to death, it went down to rank 1 over the 2-300 years.
"The Liquor worm is only a Rank one Gu worm but it is extremely meaningful to a rank 1 Gu Master, yet it's useless to a Rank two or Rank three Gu Master as they are unable to refine their primeval essence any further with it. Thus it is normal that no one paid attention to this. However, taking the initiative to expose the matter of the Liquor worm cannot be rushed for a period of time. If I overdo it, it might end up letting the cat out of the bag." As Fang Yuan walked, he pondered silently in his heart.
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Eastern · Gu Zhen Ren
A chapter later talk about a "power inheritance". This seems to be a changing vocabulary/translation issue rather of a retcon.
"Qing Mao Mountain already has no treasures left, but nearby on the Bai Gu[2] Mountain, there is a secretly built strength inheritance of a Rank four Gu Master of the righteous path.
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Eastern · Gu Zhen Ren
It starts mattering when talent cap your progress. Now FY knowledge and experience make that cap higher than for most people, but ordinarily, within the few years the C rank would be far below in cultivation while the other (say a B-rank) would have shrunk the gap in battle skills. And after a decade the C rank would be stuck while the B rank still is progressing. Even Fang Yuan in the long run, would need to find some way to increase his talent if he wants a chance to get to the higher ranks.
"He is still a C grade anyway, if he was B grade he would be another Chi Shan. Hmph, nothing to be envious about, a Gu Master's cultivation relies on their talent. If I can get a Black Boar Gu in the future, I would have even greater strength than him. That is nothing much, he can only be arrogant for a while." Some people shrugged, speaking unconcernedly.
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Eastern · Gu Zhen Ren