Humans and lockettes have an incredibly long and fraught relationship.  Doorways have put them in contact for millennia, as proven by the presence of human skeletal remains within Maquette and shell remains on Earth that defy techniques such as carbon dating.  Many myths among both species allude to one another, and there are even tales of societies that grew together or fought for territory.

Trade with humans was free and popular within Maquette for a while, but after a series of incidents that led to the Last War, they are widely hated and feared throughout much of Maquette.  The sole exception is Dimensa, which is loosely known to have reopened permanent doors to Earth after their revolution.  The locations of their doors are closely guarded, however, and those not authorized to know of them who even try to find them tend to face execution.  While Lunarimar has no laws against humans, they do not exactly have actual contact with the species.  (Although Malpais has laws against humans permanently residing there, they do allow for visitors).

Humans tend to view lockettes with horror and fear, and tend to see them as shockingly violent - many lockettes do not spare even children, when they attack - and unpredictable.  They prohibit most lockettes from coming to Earth, and it is believed their doors to Dimensa are heavily guarded - not to hide their location, but to protect against lockette invasion.

Lockettes from Dimensa are allowed on Earth, though they are rumored to undergo a vigorous visa process before they are allowed through, and must take cognitive stability tests each year to retain their visa, even if they are not traveling to Earth.  Failing even once will see a lockette barred from returning to Earth ever again.

Humans are a species from the real world, for more information on them, you may visit their wikipedia page.