What's a guardian?

Kazuma and Satsuki were frozen in surprise at the reveal Ariawyn just made. It was even enough to knock Kazuma out of his despair of losing his parents. There was one question the two of them had.

“What’s a guardian?” They asked simultaneously. Ariawyn looked at them in disbelief, especially at Satsuki. After a moment, she recomposed herself. “Why don’t we go sit down,” she said. “This might take a while.” Yuzuha lead her to the living room. Once they were all seated, Ariawyn began her explanation.

“In ancient times, there were many other races that lived in this world alongside humans,” she began.

“Their existence mostly unknown to humans, often only confined to folk tales. However, they were exposed when some of them began to prey on humans. Fearing these creatures, several groups of humans were formed to fight them. They were the hunters.”

“At first, they focused on those who threatened humanity. But some within their numbers pushed to target all other races.”

“This increase in aggression causes other races to fight back. This led to wars. Wars that have been lost to history.”

“Eventually, the other races concluded that humans would eventually wipe them out with their superior numbers. Or at the very least, they would suffer massive casualties. To avoid this, they developed a plan to leave this world for another. Once the plan was almost completed, they were approached by the hunters. They had suffered some in fighting and the victors had decided to try to establish peace. After talks, the two sides agreed that peaceful coexistence could not be achieved at that time, with the fresh memories of the wars. They decided to continue with the plan and hide the existence of the other races from humanity. The guardians were formed from the hunters to server as a third party between humanity and the other races, to ensure that neither comes into conflict, until peaceful contact could be made.”

“There is more to that story, but that is the crucial information,” Ariawyn finished.