There were originally two Gates in Hei's world--Heaven's Gate in Brazil, and Hell's Gate in Tokyo. Both appeared ten years ago from out of nowhere, and at the same time the true stars were replaced with false ones. A few days later, Contractors and Dolls started to appear as well. Five years ago, following a strange incident in South America, Heaven's Gate disappeared--along with almost the entire South American continent. Heaven's Gate is said to still actually exist, but it is now inaccessible, and the fate of those in South America at the time is unknown. Only Hell's Gate now remains.

Hell's Gate is a nightmare realm. It defies all logic and physics--it can affect biological life on the atomic level, cause all manner of illusions, retaliate against those who try to enter, and generally warp reality itself. It’s not uncommon to experience auditory and visual hallucinations near the Gate, and it is said that the Gate is capable of returning that which is lost. All manner of strange things exist within the Gate; Hei once had an experience involving stone flowers that grow like any other plant. The landscape within the Gate is also constantly in flux, which makes it difficult if not impossible to explore it, let alone find its center.

The Gate also has a special effect on Contractors. Since Contractors are intrinsically linked to the Gate, they can, to some degree, sense the Gate. When a Contractor approaches the Gate they will begin to feel nostalgic, fidgety or anxious. Prolonged exposure to the Gate can drive a Contractor insane or just generally kill them. At the same time, though, the existence of Contractors is dependent on the existence of the Gate. If the Gate were to be destroyed, every Contractor in the world would die.

Hei in particular tends to see the image of his sister, Bai, when he is near or inside the Gate. Bai disappeared along with South America during the incident at Heaven's Gate. This understandably tends to be rather traumatic for Hei.