UFO Ultramaiden Valkyrie

Plot
On a world where aliens are commonplace, Kazuto Tokino decides on his own to run his grandfather's bathhouse despite the protests from his parents. Kazuto however lacks a lot of the skills needed to make such a venture successful and must get by on a sunny disposition. That alone might have made things hard enough for him, but an alien princess named Valkyrie destroys the bathhouse, and in the process mortally wounds Kazuto. However, she is able to save his life with a magical kiss, but that kiss costs her half of her soul and transforms her into an 8 year old child, though when Valkyrie and Kazuto kiss, their souls connect allowing her to temporarily assume her adult form and wield the Key of Time, a powerful sword-shaped artifact. Princess Valkyrie is then stranded on Earth, unable to look after herself as the entire solar system is out searching for her. Over time, Kazuto and Valkyrie fall in love with each other.