Nekomi Institute student Keiichi Morisato is ordered by his sempai (seniors) to stay at the club dorm on a Saturday night to take and return calls. A nice guy that people take advantage of, he does as ordered. But when he tries to call his sempai, he dials a wrong number...and his world is changed forever.

Keiichi makes his wish that Belldandy will stay with him forever, and it becomes true! And it can't be undone; the wish has been registered with the system. Keiichi ponders what to do now, but his senpais Tamiya and Otaki arrive and find that he's broken the rules about having girls in the all-guys dorm. What will happen to Keiichi and Belldandy now?

Keiichi and Belldandy search for a place to live, trying out real estate apartment listings, his friends' apartments, and eventually a fairly worn down temple where a monk lets them in.

Keiichi takes Belldandy to his school, and all the classmates are impressed by the new girl. Sayoko, the popular girl on campus, meets Belldandy and tries to figure out where she came from. Realizing her popularity is dwindling, Sayoko tries to get in between Keiichi and Belldandy, accusing her of not even being a student, and creating situations where she and Keiichi can be alone. But the Ultimate Force that is linked to Keiichi's wish has other ideas.

Keiichi left his books and papers at home, so Belldandy goes back to get it. As Keiichi is left alone at school, Sayoko challenges him to stop acting like he's in elementary school with that relationship. Keiichi struggles on what to say to Belldandy. He sets up a romantic mood at home with candles and all. Will that do the trick? Or will it be written off as another coincidence?

A young woman shows up at the temple where Keiichi is staying. It turns out to be Keiichi's sister Megumi, who is in town looking for apartment housing. Keiichi and Belldandy help Megumi find a place, but it has a dark secret.

Belldandy learns about Valentine's day in Japan. Sayoko tries to set Belldandy up with the campus playboy Toshiyuki Aoshima. This could be trouble!

Keiichi gets a video from a store, but when he plays it, a mysterious woman shows on the screen. The woman is Urd, who is Belldandy's older sister. Urd tries to move Keiichi's romantic intentions forward by slipping him a controlling love potion.

Belldandy wins the Miss NIT contest and becomes Campus Queen. Sayoko and Toshiyuki try to uncover Belldandy's identity by setting up revealing situations where Belldandy would have to use her magic, but with big sister Urd watching, that isn't so easily done. Toshiyuki manages to put Urd to sleep by playing Enka music, and Sayoko kidnaps Keiichi. To get Keiichi back, Belldandy might have to reveal to Sayoko the truth about herself!

The Nekomi Motor Club is recruiting new members, but now there's a new rival club called Four Wheels that was started by Toshiyuki. The motor clubs have a challenge race over who gets to keep their club around. Keiichi and Belldandy get to represent Nekomi in the race, but where there's Toshiyuki there's sabotage. Can Keiichi and Belldandy pull through?

Tamiya and Otaki buy a strange Demons CD from a store. Not only is the music strange, but a spirit shoots out of the CD and asks what wish they want. Not caring they just wish her to go away. The spirit is the demon Marlier (aka Mara), and she's ready to mess up the goddesses' plans. Now that the cat's out of the bag, what will the goddesses do?

Marlier offers Sayoko a plan to get Belldandy out of the way. Sayoko tricks Urd and steals the Demons CD. Marlier casts a spell to tip Keiichi's heart balance so that Keiichi becomes fixated on Sayoko. After Belldandy goes home feeling strange, Sayoko is alone with Keiichi. This is her big chance, but what are all these suggestions Keiichi has?

More goddess-related system problems arise because of Belldandy's unstable heart. A new girl shows up at the temple, and it's Belldandy's kid sister Skuld! She's there to deal with the outbreak of bugs but also has an ulterior motive, to bring Belldandy back to heaven. To complicate things, Skuld's bug blasting invention isn't working and is doing all sorts of weird things. Can Keiichi and Skuld repair the machine in time or will Belldandy have to return to heaven?

Skuld's been spending a lot of time with Belldandy, but Belldandy still wants to go to school with Keiichi. Skuld decides to take apart Keiichi's bike, but ends up upgrading it. Megumi notices the upgrades and starts to critique it. This upsets Skuld, who issues Megumi a mechanic's challenge. At the suggestion of Keiichi's senpais, Skuld and Megumi enter a robot battle contest to settle their conflicts.

Skuld reveals her latest invention: Banpei-kun RX. Banpei is a robot designed to protect Belldandy, which he does easily as Marlier shows up for an attack. But that also means protecting her from Keiichi and Urd and draining tons of power from the house. Can Skuld teach Banpei to play nice? And what will they do when Marlier launches another attack?

Marlier's attacks on the goddesses keep failing so she goes for a new target: Megumi! She takes over Megumi's body, and solicits the help of Senbee, the God of Poverty and generally bad luck spirit.

Club member Sora is entered into an all-girls racing event. Belldandy and the gang help her overcome her fears of driving and of messing up everything.

Megumi gives Keiichi some tickets to a beach resort. Keiichi and Belldandy go, but the sisters tag along as well. Urd tells Keiichi there's an island spot where if he confesses it will be true love. Keiichi tries to take Belldandy to that remote island location, but Skuld has other plans.

Urd makes a love candy for Keiichi, but Skuld suspects something and slips in some additional ingredients. Belldandy consumes it, and she becomes very romantically bold in all her actions and with Keiichi too!

Urd and Skuld leave to do some work back at heaven. Skuld has Keiichi eat some flan which transforms Keiichi into a woman. Now he'll keep his hands off Belldandy, right? Keiichi and Belldandy go through Urd's potion ingredients to find an antidote but the formula goes wrong and Belldandy catches some kind of flu, and it's getting worse!

Skuld admires Belldandy's angel and wants to have one as well. Skuld tries training her skills with inventions. Then something ouside threatens the girls and it's up to Urd to summon her angel, but it's revealed that Urd can't because she told her angel earlier to never come out ever again. What will the goddesses do?

Mara retrieves a demonic urn from a cave. Urd's goddess license had been suspended, which motivates her to look for a regular job. But when things go bad there she accepts her demonic heritage and transforms into the Lord of Terror! Big Trouble for Keiichi and the gals!

The Yggdrasil system is in chaos from all the attacks from the Lord of Terror. Urd starts releasing the Ultimate Destruction Program which will not only destroy the current world but allow the demons to rule it. Belldandy decides to release her sealed power and confront Urd. God gives Skuld a Midgard Flute as a last-chance vaccine to stop the Lord of Terror. Will those efforts be enough?

It's the final showdown where the goddesses, Belldandy and Skuld, battle against the Lord of Terror, who has now possessed Midgard! With the whole world at stake, what can Keiichi do to help? Perhaps another attempt at the flute will do the trick, and that almost works, except now the Lord of Terror has possessed Keiichi!Could this be the end of the world? Will Belldandy be able to save her love?