Alone in his dorm room one Saturday night (a frequent occurrence, to be honest), young Keiichi Morisato accidentally dials a wrong number that will literally change his life. You see, he inadvertently reaches the Goddess Technical Help Line, and a goddess is dispatched to grant him one wish.

The lovely young Belldandy informs him that he may have one wish - a wish for virtually anything in the world. In disbelief, Keiichi opts for a wish he believes will confound the system (and will prove that Belldandy has no particular wish-granting power): he wishes that Belldandy would stay with him always.

The power of this wish almost rips the fabric of time and space but it is ultimately granted. But of course such a wish has unforseen consequences, including the fact that Keiichi lives in a guys-only dorm. When his roommates return to find him with a woman on the premises, he is immediately tossed out on to the street. But the wish also has other unexpected side effects - such as when Keiichi and Belldandy are in peril of being separated, a motorcycle is suddenly repaired so that they can travel together.

(Source: Dark Horse)