Season 1: Hei is looking for clues for what happened to his sister Bai while still working for the Syndicate dealing with Contractors with his team of Huang, Mao and the Doll Yin.

Hei's sister Bai becomes a Contractor and Hei, a normal human, joins the Syndicate along with her.ĥ years ago there was a conflict around Heaven's Gate called Heaven's War and Hei's sister Bai disappeared along with Heaven's Gate. The Syndicate is originally created to deal with this.ġ0 years ago the Heaven and Hell's Gates appear, along with Contractors and Dolls. Heaven's Gate is still inaccessible after S1, Hell's Gate is still there.ĥ0 years ago there was a prophecy detailing events that will happen in the future, part of which is like a doomsday prophecy that some bad stuff would happen when two individuals Izanami and Izanagi meet, and an entity will appear from the Hell Gate.

I assume you didn't watch the OVA? They take place between S1 and S2 and explain why Hei is an alcoholic in S2. This was one of my favorite anime back in the day.

What's darker than dark