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. 
(Source: Cidsa)

UFO Princess Warukyure, aka UFO Princess Walkyrie is about a princess from outer space who accidentally crashes on earth, where Kazuto desperately tries to maintain the public bath of his grandfather. Due to circumstances, Kazuto receives part of princess Walkyrie's soul which forces her to stay there with him. But that's not the only problem ... because her soul lost strength, the princess transforms both mentally and physically into a little kid! 
(Source: AniDB)

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