First it should be noted that the continueity of this series is a bit screwy. Episode 1 actually takes place AFTER episodes 2 and 3. To make things less confuseing I'll be describing events as they occur in chronological order.
The show takes place on Earth in an unspecified future date where humanity has come in contact with aliens who now visit our planet and mingle regularly with humans. Kazuto Tokino is a high school boy who runs his late grandpa's bathhouse. His parents (who are never shown) and younger sister Rika think he's wasting his time and that the place is doomed to go out of business, but Kazuto is determined to try to make a living of it. Then one night a spaceship from the planet Valhalla carshes on top of the bathhouse. The pilot is Valkyrie, princess of Valhalla who ran away because she didn't want to be forced to marry a prince for beurocratic reasons rather than for love. In the crash Kazuto his horribly injured and Valhalla must give him part of her soul to save him. This turns her into a child, both physically and mentally. Now she wants to stay and live with Kazuto. The next day Kazuto's old childhood female friend Akina Nanamura stops by with a cake she bought. She sees Valkyrie clinging to Kazuto. The young Valkyrie says she gave Kazuto "the most precious thing a girl can give". She means part of her soul, of course, but naturally Akina takes this the wrong way and hits him over the head with the cake and storms out. She returns to the shrine where she works as a shinto priestess, but then another spaceship crashes on top of it. Out comes Hydra, Valkyrie's more aggressive sister who has several powers including being able to fly and fire energy beams. If Valkyrie doesn't return to Valhalla and marry a prince, Hydra will be forced to marry instead. So she's come back to caputre Valkyrie and take her back home so she'll marry. She's shocked to find Valkyrie's turned into a kid, but she resolves to take her back anyway. Kazuto takes Valkyrie and runs off with her. Hydra searches town for them. Kazuto and Valkyrie hide in his old elementary school. Things are quiet for awhile, but then Hydra finds them and attacks. Valkyrie kisses Kazuto and turns (temporarilly) into an adult again and battles Hydra. Then Rika and Akina show up. Akina sneaks up behind Hydra and puts a mystic scroll on her, which turns Hydra, like her sister, into a child. Unlike Valkyrie, however, Hydra still has the mind of an adult, so she's not at all happy about being stuck as a kid again. In the end Hydra ends up living at the shrine with Akina and Valkyrie lives at the bathhouse with Kazuto and Rika.
In the next episode Ms. Sanada, the head of the Valhallian Imperial Maid Squad, comes to Earth in search of Valkyrie. She finds her at the bathhouse, and doesn't seem too bothered that the princess is now a child. In fact, Sanada thinks Valkyrie is pretty cute in her current form. When Valkyrie says she wants to live with Kazuto, Sanada declares that he will be her husband. Kazuto never agreed to marrage, however, so he's less than thrilled. Later Kazuto walks home with Akina and they reminese about old times. Then Sanada sees Kazuto buying Akina a gift. Sanada is enraged, thinking Kazuto is cheating on Valkyrie, so she takes out her blaster that turns anyone she shoots with it into a catperson (a human with cat ears and a tail, like Sanada has,) and a brainwashed slave who'll gladly do whatever Sanada says. She then begins blasting every girl Kazuto runs accross and says anything to, and by the end of the day she's turned about 70 girls or so into obedient cat girls. When Hydra finds out she runs over to the shrine and warns Akina, since she doesn't want Akina switching to Sanada's side, as Sanada cares only for Valkyrie and not for Hydra. But then Sanada and her catgirl army come to the shrine. Sanada tries to shoot Akina, but Akina uses her psychic powers to deflect the gun's beam. Akina then lifts the spell on Hydra, turning her back (temporarilly) into an adult. Hydra begins battling Sanada, but then Kazuto and Valkyrie arrive. Kazuto tells Sanada that he and Akina are just friends and there's no romance between them, so Sanada stops her attack and apologizes to Akina. Sanada then has her army work at the bathhouse. (The moral and ethical problems of having once normal women leading normal lives who were forcibly turned into catgirls and brainwashed servants remain as such is basically skipped over.) Sanada also moves into the bathhouse.
In the first episode (which, again, takes place after 2 and 3 which were described above,) Kazuto is at the air/spaceport watching the plane that his parents are in leaving. (We are never told where they were or what they were doing before, or if they even know of the presence of the three Valhallian visitors.) The rest of the first half of this episode is mostly just the different characters going about thier daily life. Then one night as Valkyrie is about to go to sleep, she tells Kazuto that she wants to play hide-and-seek the next day, and if he can't find her, she'll go back to her home planet with his soul with her. The next day Valkyrie is nowhere to be found. Kazuto, Rika, Hydra, Akina, Sanada and her catgirl army search all over the city for her, but are unable to find her. Finally Kazuto finds her at the Spacecraft Docking Tower in a docked spacecraft. Both are happy that he's found her, but as she's getting out she trips and accidentally activates the spacecraft. It flies in circles and crashes into the tower, sending debris falling. Kazuto picks up Valkyrie and carries her down the stairs that are located on the outside of the tower with him, but the falling debris destroys the stairs in front of them. Then Valkyrie kisses him and again turns momentarilly into an adult, and saves them both. Then they go home.
In the last episode of this disk, Hydra and Akina plot to use a net gun to capture Valkyrie. Akina wants Valkyrie gone because she's secretly in love with Kazuto. But thier plan backfires and Hydra and Akina end up netted instead. Then Prince Triam, one of Valkyrie's would-be suitors, arrives with his robot Aujiro. He has come to take her back to Valhalla and marry her, and is also stunned to see her in child form, and thinks she's gotten a disease from Earth and needs to be taken back and cured. As it turns out, Valkyrie ran away when she found out Triam was planning to have her do all the work while he took it easy. Valkyrie refuses to go with him, and she leaves with Kazuto. When Triam learns she's a child because she gave part of her soul to Kazuto, he has Aujiro turn into a shuttle craft armed with a blaster that will give back Valkyrie her soul, which will probably kill Kazuto. Will Kazuto survive? Will Valkyrie be able to stay on Earth with him, or will she be forced to return to Valhalla and marry Triam...?
If you're a long-time viewer of dubbed anime, you'll probably recignize a few familiar voices. Kira Vincent Davis (Miyu from SUPER GALS!, Osaka from AZUMANGA DAIOH, Najica from NAJICA BLITZ TACTICS, Rumma from SLAYERS, and Momoru from SISTER PRINCESS) is both the older and the younger versions of Valkyrie, and she gives each role a seperate tone and personality so that one could well mistakenly think that two different voice actors were doing the character. Greg Ayres (Chrono from CHRONO CRUSADE, Hokuto's lackey from CHROMARTIE HIGH SCHOOL, Shinji from FULL METAL PANIC, Leo from GHOST STORIES, and Tsuyoshi from KODOCHA) is Kazuto, Monica Rial (Natsume from the MERMAID FOREST T.V. series, Amy from CASE CLOSED, Aya from KODOCHA, Kyoko from FULL METAL PANIC, Sayaka from MAGICAL SHOPPING ARCADE ABENOBASHI, Ms. Ninamo from AZUMANGA DAIOH, Kirika from NOIR, Lila from NAJICA BLITZ TACTICS, Hyatt from EXCEL SAGA, Nanaka from NANAKA 6/17, Momoko from GHOST STORIES, and Sakuya from SISTER PRINCESS,) is Rika, Nancy Novotny (Raika from MABURAHO, Koyomi from AZUMANGA DAIOH, and Rin Rin from SISTER PRINCESS,) is Hydra, Cynthia Martinez (Lina Inverse from the SLAYERS movies and OAVs, Yuna from GALAXY FRAULIEN YUNA, Poemy from PUNI PUNI POEMY, and Kaho from SISTER PRINCESS) is Akina, Christen Auten (White Compiler from COMPILER, Princess Mirage from GALAXY FRAULIEN YUNA, and Kechiro from GHOST STORIES) is Sanada, and Chris Patton (Souske Sagara from FULL METAL PANIC, Gourry from SLAYERS PREMIUM, and Hajime from GHOST STORIES) is Prince Tiam.
If you're a fan of "harem" anime, (one guy and several different girls,) check this one out.