UFO Ultramaiden Valkyrie (円盤 皇女 ワるきゅーレ, Enban Kōjo Warukyūre?), also known as UFO Princess Valkyrie, is an anime series based on the manga of the same name, which has run for at eleven volumes, and still seems to be continuing. It was created by the manga group Kaishaku, who are also known for creating Steel Angel Kurumi.

It follows the story of Kazuto Tokino and the alien Princess, Valkyrie, who gives half her soul to Kazuto after accidentally crashing her spaceship into his bathhouse and nearly killing him. The price of her "gift" to him turns her into a child. Whenever she kisses Kazuto, Valkyrie regains her adult form for a short time, along with magical powers.

UFO Ultramaiden Valkyrie was directed by Shigeru Ueda for Media Factory Inc. and initially ran for 12 episodes. Since then there has been a two episode OVA, a 12 episode Season 2, a six episode Season 3, and a two episode Season 4. English translation and production of UFO Ultramaiden is by ADV Films. In 2008, UFO Ultramaiden Valkyrie became one of over 30 ADV titles whose North American rights were transferred to Funimation Entertainment.

Source: Wikipedia