A UFO boarded by members of the DearS species (an alien species with a human outer appearance) makes an emergency landing on Earth. Ever since then the life of Takeya, a typical male high school student in Japan, and Neneko, his female childhood friend, has been complicated by the arrival of Ren and other DearS members to their city. The DearS ship contains beings that are genetically engineered as slaves, which is why there is never any search party sent out for the disabled ship. Because the DearS are very intelligent, they do not release this to the Earth public because of public distaste for slavery. Instead, they release the completed slave models into exchange student programs, in hopes to integrate themselves into society. A DearS will imprint itself onto one person, who become their "Master." Since a DearS's happiness relies heavily on the happiness having a Master, the integrated DearS search for someone to serve. pod containing an incomplete DearS goes awry, and releases a DearS into the public. This DearS is functional, but lacks any knowledge save for her model number, which begins "Ren Ren Ren" (000) because she is not complete. Takeya saves "Ren" from an oncoming truck, and she imprints on him. The remainder of the story focuses on the chaos that results from Ren's escape and her subsequent imprinting.
~http://en.wikipedia.org/wiki/DearS

comedy ecchi sci-fi aliens