This is a theory submitted by Aliseyun!
In physics, there is a phenomenon called resonance, whereby having a body vibrate at a certain frequency, you can cause other similar bodies to vibrate in response. This process can be used to explain the goals of Ouroboros during Sen II.
Broken Theory Notes (added by Aliseyun 10/11/2017)
Sen III reveals that most, if not all of the remaining knights were awakened prior.
In the finale of Sen II, Vita succeeds in her goal to raise the Infernal Castle as well as have the Azure and Ashen knights fight at the top. Perhaps when these two knights fight with each other they give off a frequency, which would cause any nearby divine knights to give off a similar frequency. This brings up two questions however: First, the only divine knight nearby was Testa-Rossa, what is the point of having it resonate? And the second question: What data is Vita trying to gather by having them resonate?
Luckily, the answer of both questions is the same. Perhaps the Infernal Castle is meant to serve as more than just a setting, but rather as a broadcasting antenna. Valimar and Ordine would battle at the Vermillion Throne, giving off a resonating frequency, while the Infernal Castle would amplify that signal, spreading it across the entirety of Erebonia, causing the 4 missing divine knights to resonate.
Given that Vita was banished from the Hexen clan due to breaking a taboo, it is likely she was not aware of all of the clan’s information, and is possibly only privy to the location of a few divine knights. Thus broadcasting this resonating frequency would instantly reveal the location of the other knights, which are likely necessary in order to obtain one of the Sept-Terrion in Erebonia.
The last question we have is: What is Ouroboros up to after the events of the Finale? They now need to secure these knights under their control, as they will become needed in the future, and thanks to their knowledge of the Divergent Laws, they may be able to circumvent the trial system, which has kept reaching the Sept-Terrion out of humanity’s reach.