If you're looking for anime similar to Interplanetary Intercourse, you might like these titles.
Sorao is an ordinary student who lives an ordinary everyday life of a typical kid, accidentally makes friends with two aliens stranded here on Earth. His life changes as he decides to help them find a way to get home.
The Nohara family is abducted by aliens from an advanced civilization who claim that Himawari is a legendary princess who will save the solar system. Unaware of the consequences, Shinnosuke signs a contract that allows her to be raised in the alien world. This forces him and his parents to go on a desperate quest to bring her back.
Three weeks have gone by since the alien spaceship crash landed on the Graviton City spire, and since then the aliens have been hard at work converting their ship to a pleasure district, hoping to make friends with the humans! ...Not. Perpetually late and continually over-eating A-ko, spacey and cheerful C-ko, and brilliant and bold B-ko are about to enter summer break from school, and it just so happens the aliens' ship is open for business. When a free meal turns into a sob story about how the aliens just want to go home, will it be A-ko or B-ko who can get the ship into orbit again? More importantly, which one of the two will win C-ko's affections?
In 2052, mankind has spread to planets across the galaxy, living in peace and harmony. But when a mysterious vessel arrives at Earth, human life as we know it is virtually destroyed in the blink of an eye. Invaders from a destroyed planet have been searching the galaxy for a new world, and they're out to take Earth by force for their own. Now, against all odds, Colin Collins and a skilled military team must fight to save their race with the help of an experimental submarine and spacecraft.
UFOs and aliens from beyond the stars are common themes in media, entertainment, and other forms of science fiction; however, many individuals have sworn they have seen UFOs and have been abducted in real life! Sit back and watch as the makers of Mazinger take you on a journey through the history of UFO lore. Could it be that UFOs are real and that aliens watch us from afar? In the end, only you can be the judge.