UFO Ultramaiden Valkyrie

Princess Walkyrie, a celestial being from outer space, crash-lands on Earth, inadvertently disrupting Kazuto's life. As he tries to maintain his grandfather's public bath, Kazuto becomes the unintended host of the princess's soul, and she's forced to stay with him. Complications arise when her soul's strength is depleted, causing her to transform into a young child, both mentally and physically.