The Order of the Guardian is a sort of "warriors' society" in existence by 2198.
The exact connection between the Order and Tom, the Guardian of the Eggs is unknown, though certainly he will play a role in the Order's beginnings. After the Gargoyle Nation is formed, Ishimura, Japan will be chosen as the location for their school, no doubt due to Ishimura's long tradition of teaching Bushido to humans.
Humans who desire to do so, come to Ishimura to join the Order. The Order's purpose is to train young humans as gargoyle warriors, teaching them the Gargoyle Way of Protection and Service. The Ishimura Clan is responsible for guiding their human students on this path. Though they are typically taught in two separate tracks, gargoyles and humans do have classes that overlap.
The admission process is incredibly difficult for humans in comparison to gargoyles (of whom all are admitted), which will likely result in a few lawsuits. In their defense, the gargoyles are exercising caution towards any human wanting to learn their skills, knowing that they could be used against them.
By age seventeen, Nicholas Natsilane Maza will join the Order and will be one of fewer than a hundred humans to graduate to the status of "Guardian." Samson will also train as one of the many gargoyle students.