The story is about Rito Yuuki , a high-school boy who cannot confess to the girl of his dreams, Haruna Sairenji. One day when coming home and sulking in the bathtub a mysterious, nude girl, appears out of nowhere. Her name is Lala and she comes from the planet Deviluke, where she is the heir to the throne. Her father wants her to return to her home planet so she can marry one of the husband candidates, but she decides that she wants to marry Rito in order to stay on Earth.
Episode 1
Rito tries to work up the courage to confess to his long time crush. The universe seems to be against him, dropping a naked runaway alien princess named Lala into his bathtub.
Episode 2
Rito finds that he's engaged to Lala and has three days to save the planet from her alien father, King Deviluke. To make matters worse, his longtime crush is mad at him.
Episode 3
Lala is the new transfer student at Rito's school and even though he implores her to keep a low profile, her antics are making her rather popular.
Episode 4
Inspired by Mikan's hot meals, Lala tries to cook, but the results are yucky. Rito sees his chance and declares that he will not marry Lala unless she can cook well for him.
Episode 5
Saki Tenhouin, the queen of Sainan High School, becomes jealous when she finds out Lala's popularity is on the rise and challenges her to the Miss Sainan Competition.
Episode 6
Lala wants to learn more about Rito, but she may have gotten the wrong idea in science class during dissections.
Episode 7
A new rival for Lala's affections has arrived at Sainan Private High School: Ren, one of her childhood friends.
Episode 8
One of the school prefects, Yui, is all about good morality. She convinces the principal to allow her to create an enforcement squad, making Rito public enemy number one.
Episode 9
Another suitor blasts his way into the picture, this time quite literally, wearing an armored rocket suit, trying desperately to snatch Lala.
Episode 10
The president of Lala's fanclub comes to take Lala away for an idol CD, but she refuses so she needs to find a 'golden egg' to do the acting. Rito tries to stop her when the president fixates on Haruna, saying that only Haruna could work as as substitute for Lala.
Episode 11
Rito is attacked by a strange, golden haired girl on the street. It turns out that she is an assassin, know as Golden Darkness, hired to kill him.
Episode 12
The athletic festival has arrived and Rito makes a complete fool of himself, trying everything he can think of to impress Haruna.
Episode 13
King Deviluke is coming to Earth to see if Rito is worthy. Rito is left with only one option: become the Greatest Man in the Universe.
Episode 14
With Rito's Greatest Man in the Universe training underway, he runs into Haruna and they develop an unlikely relationship, which finally escalates in Rito's favor: a date!
Episode 15
Rito, Haruna, and Lala are moving up in the universe, when an alien prince visits and they each become Ambassadors of Peace from the Earth.
Episode 16
Everyone decides to have a fun afternoon together at the water park. However, Rito now has a new source of relationship drama: Run has fallen in love with him, too.
Episode 17
Rito and everyone decide to go to the old school to find out if the rumor of a ghost haunting the building is true.
Episode 18
A spaceship flies over the school and drops off a package for Lala on the roof. Inside the package is a pregnant wolf that jumps out and tries to kill her!
Episode 19
After seeing a commercial on TV promoting a hot springs, Lala tells Rito that she wants to own one, proceeding to build her own right in their backyard.
Episode 20
General Mojack decides to try and take over the world so Kirisaki takes it upon her self to destroy him by turning into Magical Kyoko Flame.
Episode 21
Yuuki hears about an alien hotel being run by Mikade-sensei and Kimio. There, Yuuki decides to try it check it out via the old school building.
Episode 22
Everyone is upset by Yui's submission of what they should do for the culture festival. She submitted that they do a region research display or a calligraphy display.
Episode 23
Saruyama wishes that he was a nobleman from the Edo Castle. He then starts to daydream about being the ruler of Edo Castle.
Episode 24
Lala's personality changes due to a fever. Rito now has to deal with Lala's constantly changing personalitues and her desire to take over the world as a deviluke princess.
Episode 25
Rito receives a message from the King which orders him to board the spaceship and prove he is the best in the universe. Before boarding, he confesses his feelings for Haruna.
Episode 26
Yuki wakes up to Haruna and Lala yelling at him that he is about to miss the ship. Lala decides she can't marry unless he wants to.
