Valkyrie, Kazuto, Akina, Hydra, and their gang return to face fresh challenges arising from the sudden emergence of the Key of Time and other perplexing events. The reason behind this seems to be tied to an individual named "Valkyrie Ghost," who is intent on possessing only Kazuto. In order to confront this formidable foe, they come together to embark on a quest to uncover the mysterious past of their birthplace, Valhalla.