Harkam's mind wanders a lot. He is usually thinking about other things instead of focusing on the meeting. He will say it is because the meetings are slow and boring. This meeting had the potential to be exciting when Stelios came and the possibility of a public execution hung in the air. It quickly became apparent that he wouldn't get his wish so he became distracted. Then he noticed that one particularly odd god is not attending this meeting.
It is one thing for the god of fate to not bother with meetings during the time of peace but they are in times of war and yet the god of fate is still not attending the meeting. Harkam couldn't help to marvel at the audacity. Of course, he had to marvel outwards not within his mind. That's why he spoke out about the god of fate's absence.
Harkam's observation drew the attention of other gods too. If not for the god of fate's seat still being around, they would think he is dead because no one has seen him for a long while. They began questioning things that they shouldn't question and some are already trying to contact the god of fate.
The Celestial Supreme schooled his face and spoke calmly, "The god of fate isn't here because I have sent him on an important and secret mission. Now no more distractions, let's get to the matter at hand."
That makes two sources of trouble that he has to put out before the meeting to put down the demon troubles started. Both troubles are related and further increased his reluctance to allow the creation of more Celestials.
The gods became silent after that and listened to what he wanted to say. His answer is not good enough for them but no one wants to question him about it. He already said that the mission of the god of fate is secret. It will just be asking for trouble by asking about it.
"We are currently at a threshold or perhaps on a cliff edge. We either overcome the next challenge coming our way or we lose the mortal realm to the demons. We have to destroy the Stronghold before it is built. In light of the seriousness of the situation, I think it is time to use the GodSlayer."
His words were met with only silence and confusion. The high, mid, and low gods don't know what he is talking about. They don't know what a GodSlayer is but they expect that things will clear up if they remain patient and observe. The grand gods know what he meant by a GodSlayer but he shouldn't know about it. It is why they are surprised but none of them showed it, not even Harkam. Harkam's reaction might just be due to him being absentminded again and not being stoic.
The Celestial Supreme continued to talk when he saw that no one wants to admit to knowing the secret weapon they were making behind his back.
"This is not a trap. I know about the GodSlayer, I know it was created by the grand gods and I know that it was designed to kill me."
The jaws of the other gods fell. The knowledge that some gods were planning a secret coup came to them as a shock. Then again, if someone will plan a coup against the strongest god in the pantheon then it had better be secret. They obviously failed since their coup isn't a secret to their target.
The grand gods glanced at Stelios imperceptibly. He was a grand god a short while back. It could have been him that couldn't keep his mouth shut. He probably traded the information with the Celestial Supreme to save his life.
Their little actions didn't go unnoticed by the Celestial Supreme. "Stelios didn't tell me about it. I knew about it a long time ago. Now, are you going to admit it?"
The gods consider the god of fate a jerk and they consider the god of order a narcissistic control freak. His refusal to allow Celestial gods has been getting on some gods' nerves for quite some time. Stelios is a very good example.
Stelios gets weak at night and stronger during the day. The cycle of power makes his strength unreliable. He can't output constant power and no one will care about his weakness during the trial of heaven. So he can't switch to the path of perfection and can't become a Celestial. He has been stuck in his position as a grand god for hundreds of origin cycles. Imagine his happiness at seeing the opportunity that Helios represents for him.
Stelios isn't the only god that has a weakness that prevents him from having a shot at performing well in the trial of heaven. Other gods are weak to fire or cold and the goddess of the night gets weakened during the day. Divinity is great but it prevents a god from using any other ability and it comes with weaknesses. Those on the path of perfection gradually eliminate their weakness until they achieve true immortality. Sovereigns can use other techniques apart from their concept but grand gods are stuck. Yet, the Celestial Supreme has blocked their path forward.
Then there is the Celestial Supreme's micromanaging. People hardly like their bosses and that's when they are being paid for their work. Gods are not being paid by the Celestial Supreme yet he gets to boss them around. He tells them what to do, how to do it, and what not to do even in matters that concern their churches.
Even the divine council that he calls grates on them. He makes it look like he is calling them for a discussion but it is really an opportunity for him to tell them what to do. They don't need to be here for him to order them around. He can send his orders to them but he just wants to see their face as they are forced to listen to him. So it is understandable that these disgruntled gods who have been boiling in resentment will decide to come together and hatch a scheme to get rid of their overbearing leader.