The Revolution are a sinister group of masked people. They are Protectors who disagree with the current way that the Protector system is set up. As such, they all wear Protector uniforms. The difference is that they all wear either a blue mask with orange eyes or an orange mask with blue eyes. The exception to this rule is their leader, Vain, who wears a mask that is blue on his right side and orange on his left.
The Revolution are first mentioned in the game after the speech by the CEO of ZTR Labs, Kyle Fitz. Principal Vicar announces that classes are on hold due to an attack on a student, Lance. Vicar tells the students that the attacker wore a mask, and is part of a group who claims they could attack again.
Later in the game, you will meet the masked man after you defeat the two gangs. The masked man will challenge you. After he's defeated. He said he will go back to Gemerald Cave and tell vain. So it means the Revolution hides in the cave.
Afterwards, you will be sent to investigate Gemerald Cave, and tells you that a detective is on his way, but that there isn't time to wait. Deep inside the cave, Vain appears between two other Revolution members, one wearing a blue mask and the other wearing an orange one. He will not fight you, but commands the two members to attack you. In total, they have ten Zenform.
Though it is possible that the Revolution members are graduated Protectors, they could be your classmates.
There are many theories so far as to who Vain might be. Some think that Principal Vicar could be Vain. The masked man could also be Keith, though he seems to have a different skin color. Here are some reasons people believe this;
1- Keith left immediately after classes stopped
3- Keith was very anxious when he needs to pack his "things", and he rushed off rather quickly.
However, Keith never takes off his hat, thus, Vain may not be Keith.