When was Shion's flashback of him and his father camping set at? In the first flashback, we see a meteor shower; since Shion was a contractor since he was born, this would mean that the false sky was already in place. To my knowledge, there are only two events that had a lot of contractors die (thus showing a lot of stars falling): One was Heaven's War, and the other is the events at the end of the first season.

When Shion's flashbacks occurred, was it during Heaven's War, or the end of the first season (which I like to refer to as Hell's War)?
The original Suou died 8 years before Ryūsei no Jemini, which is set two years after the first season. Izanamis stopped awakening in the OVA, which was 6 years after human Suou died. Logically, Suou has to have died during Heaven's War.