Scrape your jaw off the bathhouse floor and get an eyeful of the wildest maidens this side of Valhalla! Watch your favorite girls wiggling and jiggling in and out of outfits so revealing they may as well wear nothing. Except glasses! Because Princess Pharm’s in town, and she’s cruising the local high school looking for chicks that can pull off the bookish and busty look.

[Source: Crunchyroll]

The queen of planet Valhalla arrives on Earth with a virtual-world-program, called "bride training boot camp". They built several pairs which have to take a random card with a special situation that might occur if you are married. For instance Kazuto and Valkyrie have to make dinner, Raine and Kazuto's sister have to manage poverty or Akina and Hydra have to prepare a wedding ceremony as bride and groom (so everyone gets the most unlikely and unsuitable situation).

[Source: Anime News Network]

Valkyrie, Kazuto, Akina, Hydra, and friends are back for more when the Key of time suddenly appears along with many other mysterious happenings. All seemed to be linked to a person named "Valkyrie Ghost" whose only goal is stealing Kazuto for herself. As they team up against this seeming unbeatable foe they dig deeper into the mysterious past of Valkyrie's home planet, Valhalla.

[Source: Anime News Network]

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: Anime News Network]

The strange and magical events of the last season have left Kazuto with two Valkyries. He now finds himself living with and looking after both a teenaged-princess Valkyrie, as well as the child-princess Valkyrie! And they still have not yet gotten married...

[Source: AniDB]