The Dark Kind came to the world as conquerors. They failed. Now they are odd neighbors.
HeartKind bands are a way for Dark Kind (or any Deamonic/Monsterous kind) to show that people have nothing to fear from them.
As part of The Pact that ended the Six Stars Demon Wars, various places were given over to the Dark Kind. This is their neighborhood in the city.
Real world scientists have accidentally opened a tear in the fabric of reality, transporting their laboratory into the game world. Unable to repair and/or refuel their equipment in this (to their minds) primitive world they are now trapped.