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.
You find a book in the library, then when you start to read it, seems to change from pages of words to pages of images that seem to live and move. If you touch the page after the images appear, you travel into the story and now live in that world.
There is a book on that world, that leads back to this one.