From Cidsa:
A spaceship lands on a bathhouse which belongs to Kazuto's family. Inside is Princess Warukure (Valkyrie) who gives part of her soul to Kazuto to save him from death (caused by her crash).
Since she only has half of her soul, she turns into her child self. Now Kazuto and company must figure out how to fix the bathhouse and change Warukure back to normal.
