The Transforming Princess Valkyrie
Valkyrie crashes on Kazuto, and gives him half of her soul. She comes to live with him and Akina and Rika do not like it. Hydra comes to Earth from Valhalla to bring Valkyrie back and Valkyrie and Kazuto hide, but Hydra finds them. Valkyrie transforms and fights her off until Akina is able to seal Hydra.
Aired 11/07/2002EP 2 - The Transforming Princess Valkyrie
UFO Ultramaiden Valkyrie
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)