So 1972 saw Odin die and come back, and Asgard (and the entire universe) almost destroyed by Man-Gog. But remember Sif and Hildegarde? I didn’t think so.
Well, it’s time to get that story resolved. There have been glimpses of it throughout, and now we that they are on a rapidly evolving planet that was formed using a piece of Ego The Living Planet, and has developed an independent consciousness and calls itself “Ego Prime.”
Now that Thor and the Warriors Three are done with their quest and Odin is saved, they join the Sif and Hildy in the battle against Ego Prime. In the course of the battle, three of the “normal people” on this rapidly evolving planet evolve to the level of Gods and become called Young Gods–and also join the fight.
Apparently, Odin’s master plan all along was to have this happen. At least, that seems to have been his goal in terms of the Sif Quest.