One year ago, an alien spaceship crashed in Tokyo Bay. As they were unable to go home, the aliens received Japanese citizenship. They were called DearS, meaning "Dear Friends". In order to study the Japanese language and customs, a homestay system was established. One day, high school student Ikuhara Takeya encounters a DearS girl wearing nothing but a blanket. Due to hunger, she collapses on the street. Much to his embarrassment, he has no choice but to bring this alien, whom he later names Ren, to stay the night in his apartment. She insists on staying, referring to Takeya as "Master". Ren learns Japanese overnight due to her race's high intelligence and linguistic abilities and the help of Neneko, Takeya's childhood friend and daughter of the apartment manager. Later, Ren goes on to attend Takeya's school, where she is mistaken for another DearS exchange student. However, trouble occurs when the real exchange student, Miu, appears.