Shibata Youichi is an ordinary high-schooler, but one day he runs into a mysterious heroine! The cute girl knows his name, and (as in a stereotypical anime) she's an alien who needs him to help save her people! Soon enough, Youichi finds out that this situation was too good to be true... The girl, named Kyara, does represent aliens, but her people are actually interested in Japanese manga/anime/game culture. They want to use his home as a base and his brain as a measuring tool of the level of appeal of their heroines!

(Source: MangaHelpers)