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.
Game Cliche 2.
Upon learning about "the five ancient jewels" or "the nine legendary icons" or whatever, you can be quite confident that Saving the World will require you to go out and find every last one of them.