Responsible for overseeing the people from both Mistral and Grimm-folk tribes, protecting the people's safety on both "worlds" and maintaining order of both "worlds", Protectors of boundaries were established at around the beginning of (First) Mistral empire, along with the further support from royal family of (First) Mistral empire. Their most noticeable characteristics were wearing wooden/clay black-pattern mask with a pair of embedded jade-color glasses, along with pairs of green armoured sleeves and shin armours which "降惡護世" were engraved on wrist parts and shin parts respectively, meaning "subduing the evil, protecting the world".
In terms of their own equipment, the weaponry and gears they use are made of "Jade-metal", the jade-green-colored material which is strong as steel and has special property of able to disrupt, disperse and decompose Grimm-like matter produced from Grimm-folk, which the said effect is more similar to specialized medicines than general weapon in certain sense, and is apparently much more mellowed than "Brighting-silver" and "Moon-shiring herbs" Silver-eyes users use. Aside their usual weaponry like quarter staff and baton, they also made a series of inventions which provide the helpful convenience when dealing with Grimm-folk related activities, including above-mentioned black-pattern mask with a pair of embedded jade-color glasses for identifying Grimm-folk and associated status details and portable lantern made of "Jade-metal" for nullifying and decomposing Grimm-like matter produced from Grimm-folk within certain area.
Compare to their western counterparts, who usually have "killing-any-Grimm-folk-on-sight" mindset, they actually are functionated closer to be as so-called "Supernatural Police and Detective", they usually use subduing measures rather than just slaughter them when meeting the Grimm-folk tribal members, only go after Grimm-folk tribal rulebreaker while leave innocent ones alone, and generally have more friendly relationship with Grimm-folk tribes compare to the western ones, despite being limited to and more closer to "informant to enforcer" relationship. Although there were evidential appearances about sliver-eyes users joining in Protectors of boundaries, it was unsurprising for them to stay in this organization in relatively short term due to the distrust attitude from the royal family and their tendency of more violent methods.
Current status
After the certain severe massacre event caused by certain mysterious intruders, which claimed that no surviving member from that event, no one hear about Protectors of boundaries ever again, and even there are rumor said that there is still descendent from originally surviving member hidden in plain sight among current days.