Keiichi Morisato is a good-natured, yet hapless and girlfriend-less college sophomore who is often imposed upon by his elder dorm-mates and brow-beaten into taking phone messages and doing other chores for them. One day, while alone in his dorm, he accidentally calls the Goddess Technical Help Line and a beautiful goddess named Belldandy materializes in his room. She tells him that her agency has received a system request from him, so she has been sent to grant him a single wish. Skeptical and thinking someone is playing a practical joke on him, he wishes that she stay with him forever. To his surprise, his wish is granted. Belldandy must stay with him, but as his dormitory is strictly male-only, they are both forced onto the street. They set off on his motorcycle to find alternative shelter, eventually seeking cover in an old Buddhist temple. In the morning, they are greeted by the temple's sole inhabitant, a young monk, who welcomes them and gives them permission to stay until they can find permanent lodging. He immediately puts them to work maintaining the temple grounds, but when he sees Belldandy use her powers to save Keiichi from injury, he begins to fear that she may be a demon or sorceress. He is eventually convinced of Belldandy's intrinsic goodness when he witnesses her solicitous care of the temple premises and her perfect meditation ritual. When he decides to go on a pilgrimage to India, the priest gives the couple permission to remain in the temple so long as they continue to maintain it.
The Ah! My Goddess universe is fashioned loosely around Norse mythology; various names and concepts are recycled for humor. Three worlds exist in the Universe of Oh My Goddess: Heaven, Hell, and Earth. Heaven is the realm of the Lord and goddesses, Hell is the realm of Daimakaicho and demons, and Earth is the realm of humans. Reality is controlled by an enormous and complex computer system, named Yggdrasil. Each goddess is assigned Class, Category, and Restrictions. Class indicates power and skill in performing pure magic. First Class goddesses are held to a stricter standard regarding the prohibition to lie. There are also three categories: Administration, Commercial (Field), and Special Duty. Limited and Unlimited restrictions indicates boundaries on permitted actions. Goddesses may be penalized for dereliction of duty and may have their license suspended for a time. A goddess using her powers during suspension will have her license permanently revoked. Belldandy is a Goddess First Class, Second Category, Unlimited License. Urd is a Goddess Second Class, First Category, Limited License. Skuld is a Goddess Second Class, First Category, Limited License. Goddesses also wear power limiters, usually in the form of jewelry. The goddesses' purpose is to bring happiness to everyone around them. Toward that end, Heaven has created the Goddess Technical Helpline (also called Goddess Relief Agency), designed to bring happiness to the people of Earth, especially those with great virtue but terrible misfortune. A competing institution named the Earth Assistance Center, also is staffed by goddesses. In most scenarios, a goddess appears before one that the system has deemed worthy and grants him or her one wish. The wish must be approved by the system, after which a contract is created between the human and the goddess and stored on the Yggdrasil system as a file. The wish contract file is protected by a passcode known to the Goddess. As demons work toward the opposite end, the total happiness on Earth must remain in balance. Heaven and Hell strictly abide by an agreement to work through contracts and never kill each other. Demons have similar class and license restrictions, and are accompanied by familiars instead of angels. A seal exists between the demon world and Earth, named the Gate to the Netherworld. It was "created by the gods and can only be broken by an instrument of the gods." As such, demons require a catalyst to manifest on Earth. The demons possess a system similar to Yggdrasil, named Nidhogg. Both demons and goddesses possess the power to seal beings away. The demons also operate in a fashion similar to goddesses by creating contracts with humans and offering them wishes, but often at a price. A goddess does not have an angel automatically, but receives one in egg form. When her power matures, the egg hatches into an angel, becoming a lifetime companion. The angel always obeys the goddess, being a reflection of the goddess' inner self. Other creatures that exist in the Earth plane are a multitude of spirits that are responsible for almost every aspect of life. These include the spirits of Money, Wind, Engine and such. More specific entities include Earth spirits, which are guardians over a specific area of land. Morgan le Fay, a villain from the movie, is probably a high ranking Earth spirit (or a being from another dimension, but that is less likely because her tragic love story with a human must have happened on Earth) who demonstrates great strength fighting Belldandy and Urd, even though her powers are less potent than the ones of goddesses of their level.