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)

The third season doesn`t have a particular story behind everything (like "Valkyrie Ghost" in the second season). It just tells 6 stories about the life of Kazuto & Co. with some additions: Raine and Chorus get a house on earth, the last three Valhalla princesses each get an episode, and in the last episode Kazuto and Valkyrie, who in the same episode managed to stay adult, >try< to marry again. (Source: ANN)

Fantasies and miracles never interested Ayu Tateishi, a popular second-year student at her middle school. She was content with preserving her image of being cool, calm, and collected—all to catch the eye of her crush, Tetsushi Kaji. Ayu's carefree youthful days are interrupted by the appearance of Nina Sakura, a new transfer student who turns out to be a witch. As the only person who knows about Nina's ability to cast spells using a mini-computer, Ayu is forced to help Nina with her mission to find the five Holy Stones, qualifying her to marry the prince of the Magic Kingdom. Unfortunately, Nina's ineptitude with magic and her habit of meddling in Ayu's personal life cause nothing but trouble for the two of them as Ayu toils to maintain her good reputation and Nina struggles to hide her secret from the discerning eye of Hiroki Tsujiai, Tetsushi's best friend and an avid fan of manga. And when Nina's search for the five Holy Stones brings allies and challengers from the Magic Kingdom, Ayu is dragged into a world she never even dreamed was possible. [Written by MAL Rewrite]

Touta Konoe is an ordinary boy raised in a small rural town. His mundane life suddenly changes when his mentor, Katherine McDowell, reveals herself to be a vampire; after saving Touta from a mortal wound, she causes him to become immortal as well. Already yearning to explore the world, young Touta finally puts his dream to ascend to the top of Amanomihashira—a tower that leads to outer space—into realization. Along the way, he finds a secret society filled with immortals just like him called "UQ Holders." Gaining new comrades and mentorship along the way, Touta embarks on his own unique, magical adventure. [Written by MAL Rewrite]