The following contains spoilers for The Mighty Thor at the Gates of Valhalla written by Jason Aaron, drawn by Jen Bartel and Ramón Pérez, and colors by Matthew Wilson.
The Mighty Thor is dead. After wielding the power of Mjolnir for years, Jane Foster's thunderous persona met a heroic end while Jane was allowed to live and recover from her cancer. But while Jane defeated many enemies of the Goddess of Thunder, there's one she wasn't quite able to put down, and that's the Dark Elf Malekith, who's been waging war across the Ten Realms since she first grabbed the hammer.
Mighty Thor at the Gates of Valhalla sets the stage for the war to begin in earnest, through two stories that complement one another. The first tale, “The Tomorrow Girls,” is a time traveling journey involving the future grandchildren of King Thor. In actuality, we've seen Frigg, Ellisiv, and Atli before, back when Thor had to fight the God Butcher Gorr and accidentally met his future self and incoming descendants. The trio of thunder goddesses, using time diamonds stolen from their sleeping grandfather, wish to be taken back to the "Golden Age of Thor," but since the name of "Thor" has typically meant the Odinson, they accidentally wind up billions of years in the past... and get into a fight with some trolls.
Hopping through time, the girls stumble across various moments of their grandfather's youth, from one of his many failed attempts to pick up Mjolnir to the Thor of the 26th Century--they briefly make eye contact with him, much to his confusion--and even to Odin's time as a prehistoric Avenger, and we all know how that will turn out. Their time hopping even takes them to a moment that we haven't seen yet: an older King Thor decked out in silver armor with Mjolnir and fighting Loki, who is covered in all black and using an unidentified power. It's the future of the granddaughters, but before they can help their grandfather, they're whisked away to present day New York. And it's there where they meet the Thor they've been looking for all along: Jane Foster.