UFO Ultramaiden Valkyrie 4

In spite of his parents' objections, Kazuto Tokino decides on his own to run his grandfather's bathhouse in a world where aliens are widespread. Kazuto, however, lacks many of the abilities necessary to make such an endeavor effective and must rely instead on his positive outlook. That might have been difficult enough for him on its own, but an extraterrestrial princess by the name of Valkyrie also injures Kazuto fatally while destroying the bathhouse. Although it costs her half of her soul and turns her into an 8-year-old child, she is able to save Kazuto's life thanks to a magical kiss. However, when Valkyrie and Kazuto kiss, their souls connect, allowing Valkyrie to temporarily assume her adult form and use the Key of Time, a potent sword-shaped artifact. The entire solar system then goes on the hunt for Princess Valkyrie, leaving her abandoned on Earth and unable to care for herself. Kazuto and Valkyrie develop a romantic relationship over time.