The current trend seems to be that the Holy Sage and /or the current Emperor are evil or linked to the Fire people. But I believe they are just victims of traditions (and something else):
Holy Sage
1. During the Chagum's funeral ceremony, we seem him looking to the Emperor's family with sad expression. And when he receives the message that Chagum died in the mountains, he is shown sighing, giving the impression of great pain. All the people around him are just servants, so it would be irrelevant for him to "fake" his reactions.
2. If he is a disguised Fire people, then why he didn't translated the holy book by himself? And if the couldn't (due to some restriction), then why didn't allow Shuga to continue? And if he did indeed already read those tablets, then why ask Shuga to do it? -In either case, there is no gain for him.
3. When Sagum dead is uncovered, we hear his thoughts, regretting of having focused more in internal politics than he should. He truly believes that. That's enough to discard any links with Fire, or him being the puppet master. And that also explains why he gives his support to Shuga: He realized that at the end, he had become just an obstacle and that the only one capable/that "deserves" to solve all the mess, is his disciple.
Emperor
1. He never sent the hunters to assassinate Chagum. Remember that in chapter 1 is revealed that the only one that can do such task, is himself (with the old holy sword). It's reinforced at least twice later. So the persecution was not a simple&dirty way to get rid of his son - it really had a motive larger than just petty politics.
2. His behavior depict him as an honest, concerned Emperor. His grieving for both Chagum and Sagum deaths seem quite genuine. He even goes through the problem to request the build of a new statue for his son, even though it goes against the traditions and status quo. It was not necessary, so it wouldn't benefit him, if he were a puppet/dupe from Fire people.
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We can also rule out Shagum. He really cares for the prince (it was under his charge for several years, after all). And Sagum is already dead.
Couldn't just be that all of them trully believes what the Official story says? It have been hundred of years since such events occurred, so why would they need to believe otherwise?
They are only reacting to the "demon possession" + drought sign. All the information regarding the matter is seen as holy, so what else could the Emperor do? He thinks that killing his son, as harsh as it sounds, it's the only way to prevent the annihilation of all the reign. It's his duty to protect the people.
The only hope lied on the tablets, but all went to the drain when the prince was taken away by the bodyguard -and later perished during the persecution.
So, for all of you that really want to find a conspirator, think: if none of them are truly suspects.. who else would benefit of all these events? Who would be so devious, as to even use the "possesion" as a way to get rid of Chagum, fully knowing that Sagum was really sick. Was really such sickness.. natural?
Yeah, it might still be someone that we haven't considered yet.
And just for kicks: The anime has taken some length into "flesh out" the personality of 3 of the hunters. Mon as leader, seems quite honorable. Jin is heavely linked to Chagum. And the big guy has also shown traits of being an honest person.
But what of the others?
If someone in
high position in the Palace really wanted to push his agenda, wouldn't be useful to have an ally with the ultimate skill of a spy? You know.. the ability to quickly memorize documents..even if they were confidential?
Who knows. Maybe the Mon//Jin/big guy may have to face an unexpected enemy, not Balsa herself. And also maybe, the egg eater was more cunning that we initially believed.