The plot of the manga (and of most OMG series) centers on a good-natured, yet hapless and girlfriend-less college freshman named Keiichi Morisato. He is often imposed upon by his elder dorm-mates and brow-beaten into taking phone messages and doing miscellaneous chores for them. One day, while alone in his dorm, an attempt to relay a message to one of his senior dorm-mates is surprisingly redirected. To his surprise, he discovers that he has actually dialed the number of the Goddess Technical Help Line (literally translated as Goddess Relief Line). Before he can explain his error, a beautiful goddess named Belldandy (Japanese transliteration of the Norse Verdandi) materializes in his room. She tells him that her agency has received a system request from him, and has sent her to grant him one wish. Keiichi is skeptical, thinking it more plausible that his dormmates are playing some manner of practical joke on him. He seeks to defuse the prank by asking Belldandy to stay with him forever, thinking that when the wish was refused, as it must be, he would have turned the tables on them.
Keiichi's wish is granted, but he soon discovers a downside: Belldandy must live with him, but with his dormitory being strictly male-only, they are both forced onto the street. Keiichi's motorcycle had just been repaired, so they set off to find alternative shelter. Their attempts to stay at various friends' houses are constantly thwarted, so when a fierce storm strikes the pair, they are left no option other than to seek cover in an old Buddhist temple. The next morning they are greeted by a young monk; the sole inhabitant of the temple. He welcomes them and allows them to stay while until they can find permanent lodging elsewhere. He immediately puts them to work maintaining the temple grounds. When Belldandy uses her powers to save Keiichi, the priest begins to fear that she is no ordinary girl, suspecting she may be a foreign demon or sorceress. He investigates further, but is eventually persuaded of Belldandy's intrinsic goodness when he witnesses her solicitous care of the temple premises and her perfect meditation ritual. After he decides to go on a pilgrimage to India, the priest grants the two lovers permission to remain in the temple contingent upon its good maintenance. Due to luck, or perhaps divine intervention, the two now have a home.