A journal I guess

On the topic of Revenants and the Loop.

There appears to be some confusion regarding Revenants and the Collective, including what the ranking system between "regular" servants and Revenants are. 

There isn't an official ranking system to speak of. He does not have time to nitpick every single thing, including your flaws and strengths. Therefore, the hierarchy is determined by the Servants themselves. Those who are powerful, will naturally be in higher positions. And those who are not, well, it's a dog eat dog world. 

Imagine a harem. It's an odd terminology, but it's rather close to how the ranking system works. Anyone is able to replace someone in any position, so long as they have sufficient power to do so. There are those, however, which are untouchable. Revenants. Unlike "common" Servants, Revenants have mutated into non-human forms. In other words, the Ichor has caused them to turn multidimensional. They will often have unnatural traits and abilities such as extra limbs, time manipulation, omnipotence, or something along these lines. However, He will never allow them to become more powerful than Him. One single Revenant of course cannot go against the Fears. But pair their unique abilities together and you get an unstoppable force. The Collective. 

The Collective was established as a force of regulation for the timeline. They were unique Servants capable of inhabitation, much like Habit. They would monitor other Revenants and ensure all went according to the Game. All Fears have a force of special Servants like this; however they offer their own abilities which the Tall One's Ichor cannot do. Collectively they serve, or rather served, to maintain balance. That is, until the inevitable happened. 

The riots began suddenly one morning. These special forces were going against their masters; demanding more power, more freedom. The Collective were the cause of it all. I can hardly blame them. Immortal life becomes tiresome. Once you become a Revenant, there is no going back. You will never die, nor truly be alive. On that day, that dreadful day, the Time Rift opened. 

Nobody truly knows how it came to be. The Bleeding Tree is said to be malfunctioning, and so the Path is unstable. Many suspected sabotage. However, no culprit has been found to this day. The Fears came together, and in order to take advantage of the situation, created the "loop." A foolproof method of keeping rogue Revenants like the Collective in check. It is an elaborate prison; the loop contains them and prevents them from reaching full power. It is the only method known to truly stop Revenants. However, the loop is also easily broken if something significant goes off track. For example, a certain journal being opened and read, or coming into the possession of unwanted people. 

This loop, paired with the Time Rift, is what keeps us trapped here. It is the reason why we can never truly die, why we return here as different people who still meet the same fate. Time is not, and will never be linear here. With every loop reset, or "timeline shift," the memory of civilians are reset. Servants maintain their memory, as they serve specific purposes. That is why it doesn't matter what I tell you, or who I kill, and what I do. Nothing matters. So long as it isn't anything life changing which puts the loop at risk, you will forget it rather quickly once the loop resets. 

For some last minute clarification (if you are still confused,) the Collective are a branch of Revenants who used to serve as special Servants. Human Servants are replaceable (for the most part) but Revenants are not. I hope this has cleared up the misconceptions.