In my new story, Norse mythology plays a major part, going from the names to the real story. So, for the unknowing average reader, here should be some clarification:
Aesir: The gods. Some of them are called Odin, Freya, Thor, Tyr, Frigg, Loki...
Ragnarok: The end of the world. A final battle against the forces of evil. Almost all of the Aesir die. The world starts all over again, with two new humans after that.
Valhalla: Hal of the Fallen. The fallen wariors Odin wants by his side during Ragnarok go here after they die, but this heaven isn't for everyone.
Yggdrasil and the 9 worlds: Yggdrasil is a tree, and all of the nine worlds are within it. The humans live in one world, the Aesir in another one (Asgard), the ice giants in another one, the dwarves, the elves...
I really hope you'll enjoy this story!