Nibelung is Irmin
Irmin's goal is to destroy Teyvat and remake it.

All sovereigns are currently alive and in their respective regions somewhere, except the electro dragon.

The moons are abyssal satellites.

The dragon moon was black and was never raised into the sky because the moon goddesses disappeared.

The moon goddesses were seelies and they conspired with the dragons. They were killed by the moon hunters.

Hroptapyr was Irmin's body double and the betrayal of the sinners was planned, Irmin is Pierrot.

The sinners are still cooperating.

Fifth sinner Moonhunter Rerir is a mole.