Stoirm Gunainm
Stoirm Gunainm (or Nameless storm) is the name of the conflixt that took place when Tanitris was founded and modified.
Silence before the storm
Around the time when the first roots of Tree of Tanitris were founded and the city of Tanitris became more stable, the chief architect of Tanitris -- Master Tamer of Aeter was looking for means to expand and stabilize. He needed something that would respond to the threat of unknown. An opportunity appeared in which he found a group that shaped the unknown -- Tamers of the Void. With their help the thirteenth root of Tanitris was founded and the city became much more stable.
Around that the time, when the tree would be planted and the plan finalized, people gathered twice a year:
The summer solstice meeting was less formal and in the initial phase, each master/group ascended Tanitris through their respective root. The plan of the Master of Aeter was that the tree be finally made into one, so they all would be able to ascend safely in the same spot and perform skirmishes from there, expanding Tanitris even more, maybe adding more roots for stabilizing if the need appears. Ascending at the same time would not be possible without the Mòran mar aon (the hive mind) but since everyone knew eachother and their respective specialties from a long time, it was not considered a priority at that time.
The plans begin to surface
For the Tamers of the Void formation of the hive mind was detrimental to their plans. During Mòran mar aon the risk of their plans to surface would make it impossible to execute the plans of taking down the Tree of Tanitris and the Tanitris itself. There are rumours that in the end the battle took place after the Mòran mar aon was put into use and that during the initial ascent, the weaker Tamers of the Void were killed by their own to avoid leaking of their plans. This cannot be confirmed thugh and is a guarded secret of the Tamers of Æter. What is known is that around the time of the first group ascent, the Tamers of the Void began regrouping and preparations were made beforehand, even in the Ædean Realm.
The first ascent
The seeds are sown
One of the reason the plans were not found out was that during the creation of the root, when the two Masters got to know each other, the Stoirm Gunainm planted a void pocket in the heart of the Architect. Whether the one was aware of it or not is not understood completely, but many point out that a person of his caliber should be aware of the process and that most probably it was intentional, probably a way of understanding the Void itself. It is not known whether the Void pocket was planted or simply utilized. Some say that each person shares their own pocket of Void in their heart and that everyone is capable of folding into nothingness, but few are able to understand the Void well enough to feel it, let alone prove it, or utilize it. Within the pocket Stoirm Gunainm planted his intentions to destroy the Tanitris and the Tree of Tanitris. It was only after the ascent, and around the dissociation of the Mòran mar aon that the plans were taken out of the Architects heart. Shortly before his dissolution Stoirm Gunainm mentioned to the Architect that the intent was in his heart all along. And hinted that all the answers are in the Void. The Master Architect started having dreams of doubts. Dreams of destruction of Tanitris of how they would lead the world an all of its inhabitant to destruction. He dreamed of having siblings and friends who died of the malformed world, unable to understand what was being done to them.
Clouds gather, the battle starts
The summer ascent
The first ascent took place around the summer solstice, when the days was the longest. It helped to ease peoples minds and everyone was eager to celebrate the new exciting ideas they would recover from the Ædeos. They boasted of what they would do with them and how famous they would become. Some thought about pushing the limits of the society but many thought of their own and their tribal gains. This all made the first ascent very loud and all the easier for the Tamers of the Void to hide their intents. While most were easily taken care of -- the Stoirm Gunainm took their intent and hid in the Architects heart, some could not be found beforehand as they took off to find places to train of their own. These were the Masters of the Void as well, the first Tamers of the Void, who later were put together with the Great Master of the Void to form the Stoirm Gunainm. They became the first victims as shortly before the ascent their minds were blanked by the Void and then severly damaged by the Aeterial motion.
The first ascent became a scavange hunt shortly after setting thought in Ædeos. Most of the Masters dispersed and it was difficult to gather a thought at ease, since everyone was linked and extremely eager due to the summer solstice. Later on this became its undoing as the pocket was opened and the intent taken back. The Architect felt a flow of the stream of consciousness but could trace it only to the several roots. The intent was a mixture of feelings and thoughts known and unknown to him, so he could not understand all of it at first. He thought that it was the second thoughts and the dreams he had in the coming weeks.
First strike
First masters disappear or fall into traps of the Tamers of the Void. The ritual is made in such a way that it is dependent on the light and so cannot be stopped artificially.
Retaliation
The opponent is not known by name, so all the roots are severed and everyone is gathered in the center of Tanitris. Some culprits are found within older branches/roots but among them is the root of Void. Some people are killed, the ideas in their minds secured, some scavanged. Some secrets reveal a pattern difficult to understand. Masters think about them and come to some conclusion.
Second strike
While the nature of the conclusion is debated a second strike is made and now it becomes evident that the Tamers of the Void are behind the attack. A battle arises between them and the Tamers of Æter. Other schools help in their respective ways but it becomes very risky -- the potential risk is death of their ideas and knowledge gathered throughout the years. Some decide to run away to save tehir thoughts, self and knowledge.
Fallback
Many run away and the Tamers of Æter help to create a safe hrbour of unkown ideas -- pockets. It becomes a moment of enlightenment to the Architect, who uses this idea, to get to the Stoirm Gunainm and to everyone connected to him. Before that happens, a plan is devised. In that time the destruction of Tanitris is slowly starting. The Tamers of the Void begin to use their root to tame the Void onto the Tanitris and the Tree of Tanitris is slowly beginning to run trough the Void.
The (un)necessary sacrifice
The Architect is given a choice of sacrificing Stoirm Gunainm and all, who accompany him in order to save Tanitris from further decay or let the ideas form it and remake the city in later time. With how the things progress the probability of destroying everything is very high, although the decay is slowed down significantly by several roots, especially since tey work together. It is much more difficult to destroy something deeply rooted in several ideas and being very complex. The main destruction takes place near the Root of Aeter Taming. Should that root be destroyed people would need to either find an unknown yet path or somehow find that idea again -- there were nt that many Tamers of Æter in that time, which understood the concept well enough to enter Ædeos in the same place. That was the idea behind making the root all along. The decision is made to sacrifice the Tamers of the Void and utilize their ideas to stop the decay. It is difficicult for the Architect since upon ariving he understands that the dreams were thought of all the Tamers of the Void before him. These were their realities and not the consequences of what would happen but of things that were already happening around the world. The sacrifice was needed to be made though, for the sake of progress.
Aftermath
All of the Tamers of the Void were sacrificed and their ideas were modified to accomodate only for the passive role of sight. The root of Taming the Void was remade to accomodate the Sentinels of the Void only. The Masters agreed for the ritual to be made around the Winter Solstice, when the fire would be made and put out at need. The incident was masked and hidden by the Tamers of Æter so it would not be repeated again. The position of the secret is a guarded secret and known only to the Architect and the Master of the Aeter Taming. Lastly, the Architect has dissolved/shared his power to the people of the Sáveni -- he took off for a journey around the land and dissolved his cloak of the Master of Aeter Taming, after which his identity is lost to the history. After that, the people had the power to shape their own reality, although not directly as was done before, when Ædeos was entered, but rather indirectly, throgh pressure and a system of conncetions to one another. Ever since these days, it is the people most strongly reveared by the people, who are typically chosen for the Bloom festival. Takng anyone else would not only result in resistance of rooting the new ideas afterwards but would make it difficult to convince the people of the fairness of the process, creating even more resistance.
I know this is only a first draft, but it looks like you have all the important points mapped out. I am looking forward to seeing how this develops.