WARNING: The following contains spoilers for King in Black: Return of the Valkyries #1 by Jason Aaron, Torunn Grønbekk, Nina Vakueva, Tamra Bonvillain, & VC's Joe Sabino, on sale now.
Jane Foster has had many jobs during her time in the Marvel Universe starting as a nurse, then doctor, and eventually gaining the mantle of Thor. Now Thor is back being himself and Jane has taken the job of Valkyrie, demi-goddess, and guide to the dead. When Brunnhilde, the last Valkyrie, died there was no one else to ferry the dead from Earth to Valhalla. She appeared to Jane and asked her to take the job as there was no one else left. Jane accepted and has become acclimated to the role, and she might be getting some back-up.
Just as she was getting used to the role, Knull and his symbiote army attacked Earth, blanketing the planet with symbiote goo. The Sentry was one of the great heroes that was supposed to protect everyone from the King in Black but was killed moments into the fight. While Jane Foster took his spirit to Valhalla, they came across another Valkyrie trapped in a strange type of limbo. A Valkyrie who remembers being part of a force and when she is saved, Jane is no longer the only Valkyrie.
The new Valkyrie remembered being one of "the original nine" that "raised a glass at the first feast in Valhalla." Much like the Valkyrie from the Marvel Cinematic Universe, she has a drinking problem and wants to forget the past where she could not save her girlfriend from death. When Jane stumbled upon her, she was in a cycle of drinking and fighting while snippets of the past filtered in. Images like all of the armored Valkyries flying on winged horses into battle against a shrouded figure paraded through her mind. When Odin was a boy, the Valkyrie were a force to be reckoned with. Jane alone is powerful, fighting against villains when the time calls for it, but imagine what many similarly powered women could do together. The discovery of Undrjarn the All-Weapon, a weapon that can turn into anything the wielder needs it to be, is just a piece of how strong they could be.
Looking back on the original character Valkyrie's first appearance, there was another power in numbers theme. The Avengers #83 by Roy Thomas, John Buscema, and Tom Palmer featured a new Valkyrie character whose mission was to "finish off male chauvinist pigs" by recruiting a team of only female superheroes who kept getting pushed out of the spotlight by their male counterparts. Reflecting the feminist movement of the time, the team was to be called The Liberators.
At the end of King in Black: Return of the Valkyries #1, two Valkyries are united and flying together to save the soul of the Sentry that was taken into the limbo nightmare. It is worth noting that the cover of the issue shows four Valkyries, led by Jane Foster. Once they save the Sentry, the two may recruit new members or possibly resurrect old ones. Working together, and with the powerful weapons of Asgard, they could do real damage against an enemy -- even one as powerful and god-like as Knull.