A mysterious extraterrestrial girl named Lala runs away to Earth in order to avoid daily arranged marriages set up by her father, the king of her home planet Deviluke. Due to one of her own inventions, she teleports naked into fifteen-year-old Rito Yūki's bathtub, and he accidentally feels up her breasts. It is later revealed to him that this is equivalent to a marriage proposal on Deviluke, and Lala happily accepts to become Rito's future bride. Rito, on the other hand, harbors feelings for a girl in his class named Haruna Sairenji, and does not want anything to do with Lala.

Rito discovers from Zastin, Lala's uncle and leader of her personal guard, that if he were to back out of his engagement with Lala, that he would be killed and Lala's father would destroy the Earth. Rito hypothetically asks him if it were somehow possible to back out of his engagement and not suffer the repercussions. Zastin tells him that he must feel up Lala's breasts once more within the first three days of his engagement in order to call it off. While he attempts many times to touch Lala's breasts, he does not make it in time, and thus is stuck with the engagement. The next day while at school, a new transfer student is announced to the class. Just as Rito is thinking that school is the only place that he can breathe anymore, Lala is brought into class and all of Rito's hopes of a quiet school life fall apart.

Rito is devastated to hear from Haruna that she thinks he and Lala are suited for each other. At home, his younger sister Mikan notices Rito's depressed look and suggests that they should go out the next day to show Lala around town. While out, Lala's artificial intelligence helper Peke loses most of his energy, and due to this, Lala's clothes start dissolving. They head into a store and buy her new clothes, and while there run into Haruna. Together with Haruna, they go to the aquarium together, but their time is cut short when Lala makes a large disturbance which sends torrents of water throughout the halls.

Rito gets scared when Zastin tells him that Rito will one day be the king of Deviluke due to his future marriage with Lala, and that he will have to participate in interstellar wars. That night, Lala cooks but the food is dreadful. In an effort to try and get out of one day participating in wars, Rito shouts that if he will not marry Lala if she cannot cook. Lala quickly leaves and goes back into space, but appears again the next day at school with the intention of cooking something good for Rito. She collected ingredients from all over the galaxy which are still alive and reek havoc in the school. Lala later explains to Rito that he does not have to go to war if he does not want to, and even her father did not join in on the battlefield lately. To further reassure him, Lala tells him that after they get married, she intends to live with him on Earth.

A pretty, rich girl named Saki Tenjōin comes back to school and finds out that other boys prefer Lala's beauty over her own. She gets really angry by this and tells her friends to give Lala a letter asking to challenge her in a beauty contest. To make sure she shows up, she kidnaps Rito as bait. Lala ends up telling Zastin about the letter, which he mistakes as an assassination attempt from Saki. Rito, still kidnapped by her, is warned by her that if Lala fails to show up in time, he will be forced to touch her breasts in front of the entire school.

A shape-shifting alien assassin comes to propose to Lala. However, he changes himself into the principal and takes Haruna hostage in the gym equipment room. There, he uses tentacles to feel her and lure Rito to the room. When he gets there, the alien tells him that he will give him Haruna if Rito cancels his engagement with Lala, but Rito does not go along with his plan. After Lala arrives, the alien shape-shifts again and becomes much large and intimidating, but Rito stands his ground and attacks the alien head-on which makes him reveal himself as a weakling who has many wives and families across the galaxy.

A childhood friend of Lala, Ren Elsie Jewelria, arrives on Earth claiming he is manly enough to marry Lala. He constantly attempts to impress Lala by showing off his strength, speed, and looks, but all his efforts are in vain. After failing many times, Ren asks Rito how he is able to be manly enough for Lala. Ren watches a movie (Rocky VII) about how to be a man, and he works out non-stop in order to get Lala to love him. Eventually, Ren completes runs a 120 kilometer marathon and goes to Lala to hear her finally tell him how manly he is. However, at this time, he sneezes, causing him to turn into Run, a girl. Apparently, whenever Ren sneezes, his body and mind change genders into the innocent Run, and vice versa, due to his species carrying this inherent ability.

A school student, Kotegawa Yui has had enough of the "ecchi" in the school, and tries to set the school some morals. Not only does she try to clean it up, but enforce some new school rules, and has a squad so to speak, to check on the students. Shortly later, Yui has started to realize that Rito is behind all the "ecchi" in school. So she gives him punishment so he wont be able to talk to any girls for 2 weeks (well after persuading the peverted principal of course). But Yui comes to see that Rito isn´t like that, and then removes his punishment. Yet things go badly wrong when Lala's machine pulls him to her.

A guy with a rocket suit comes for Lala. The Rocket Suit guy constantly tries to attack Lala to grab her back with him but fails to do so many times. Lala gets mad at him and tries to kill him. He breaks down his armour suit and walks around the streets at night for advice. He even askes Ren for advice. Mikado-sensei finds him and heals him and he attempts in kidnapping Lala by making her drowsy and paralyzed...

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.

An assassin known as 'Golden Darkness' comes to earth to attack Rito according to her client. Rito meets her in the streets and offers for a Takiyaki. She then starts attack Rito rapidly and Zastin comes to the rescue. Sadly, he fails to do so making Lala replace him in rescuing Rito.

A perverted day for Rito at a sports festival, he keeps on accidentally touching Haruna and he thinks she hates him. The contests dont make sense and the principal makes the girls do things just to please his sick desire. This day gets worse and worse for Rito.

The day starts out like any other day for Rito, Lala right up in his face. This morning Zastin is at Rito's house to speak with him. He tells him that Lala's father is coming to see him to make sure that he is worthy of marrying Lala. Throughout the day Rito worries about what Lala's father looks like and can't get it out of his mind. Today at school all of the girls that have appeared throughout the other episodes seem to make his day "interesting." Rito gets called to the roof to speak with another girl that is introduce in this episode, but after he gets done talking to her he hears a mans voice. The woman was a test by Lala's father to see if Rito was worthy, but he fails. Rito, after seeing a little kid standing in front of him, doesn't believe that this is Lala's father. He soon shows why he is the ruler of the universe. Lala runs to the roof before anything can happen and saves Rito. After seeing his daughter protecting Rito and telling why she loves him, King Deviluke challenges Rito to become the number one man in the universe. Rito goes home and thinks this over and decides that he is going to do it.

After thinking about what Lala's father said to him, and the challenge that lies ahead, he brainstorms ideas on how to become the number one man in the universe. He starts training and meets Haruna, walking her dog, Maron, during his first run. After explaining to Haruna that he must change, she decides to cheer him on, meeting everyday during his runs. His goal to change also affects Haruna, who eventually asks him on date to eat lunch together at the river bank. During that time, Haruna's dog chased a bird and eventually lands into the river. After Rito saves him, the two go to Haruna's house to clean Rito's wet clothes. While waiting for his clothes to dry (Rito ended up wearing a towel), the two talked about their middle school days. When Haruna was about to go to check if Rito's clothes were dry, she trips. They almost kiss, only to have Haruna's older sister walk in on them, and it turns into another awkward situation when Rito's towel falls off.

At school Zastin accidentally revealed the secret about Lala being an alien. Zastin also takes Lala, Rito and Haruna to space to be ambassadors of peace. They meet an alien who challenges them to a hunt. The winner wins the title of The number one hunter in the universe. They encounter dinosaurs, Amazons who wished to marry Rito and a giant gorilla "Ginga Kong" which Haruna tames. In the end Haruna wins the title as The Number One Hunter in the Universe

The episode begins as Rito and co. all go to a water park. Run believes it's her time to make a move and further her relationship with Rito. She attempts many times throughout the episode to obtain Rito's attention, such as she tries to lure him towards her with a fishing pole, sneaking up behind him as he's bringing back ice cream, using a vacuum to pull him away from a waterslide, and even by using fiber eating fish to eat away each of the girls bikini tops in order to scare them away from rito. All attempts fail however, sending Run into a state of depression. She encounters Montemitsu who then buys her food. Run then enounters rito's teacher, who she then requests from him to teach her the ways of becoming famous, for Run now decides she wants to become a famous idol. After rigorous training, Run decides it's too hard of a feat to accomplish. She then gets attacked by some people, which then Rito shows up to save her. Lala defeats the attackers using one of her inventions. The episode closes as everyone leaves the water park, and Run states that her fight for love has only begun.

A haunted school building is shown at the episode's beginning. Lala, Risa, Mio, and a frightened Haruna are seen conversing about ghosts and monsters. Lala then suggests that the four of them and Rito should go explore the haunted house. As they all enter the buildling, a lock closes behind them by itself. They continue to explore the old school and hear what sounds like approaching footsteps. Rito notices Haruna's fright, and tries to leap at the approaching figure, only to find out it's Yami-chan. They then hear a piano which chases after them. Yami slices the piano into pieces and everything seems alright. But a skeleton and a disfigured looking human then appear, constantly saying "get out". An octopus creature appears, which frightens Haruna to such an extent that she uses Rito as a weapon and deals a mighty blow to the creature's head. The other monsters then show themselves to the group, but this time with no hostility. They explain to the group that they are aliens from other down-sized planets that have gathered in the old building. Mikado-sensei appears and tries to help the monsters find a job in order to make a living for themselves. Also, a ghost girl named Oshizu appears and explains everything about herself to the group. Mikado and the monsters appear again to tell he group that the person they talkto for hiring only wants female monsters, which none of the monsters are. Oshizu then teaches them how to be more feminine, and the monsters are then accepted for their jobs. Lala, Rito, Yami-chan, and Mikado are then invited to a party where all the monsters are. The episode closes as Lala and Rito are astonished to see Zastin attending the party.

Mikado-sensei hears a spaceship flying towards the roof of the school and decides to check it out. It turns out it's a package for Lala, so Mikado tells Lala to check it out. Lala, Rito, and Saruyama go to the school roof to check out the package, and as Lala opens it, a giant wolf jumps out and attempts to kill Lala. The wolf then suffers stomach pains and explains that she's pregnant, and that she accepted a mission to kill Lala before she knew her pregnancy would become a problem. Rito, Saruyama, and Lala are apalled to hear this, and so they take the wolf mother to the school infirmary. Saruyama is then left in charge of taking care of her while she's giving birth. Lala believes the wolf mother deserves a souvenir as a gift for her child's birth. The wolf mother then tells Lala that she wants Saruyama as her gift. After hearing this, Saruyama angrily declines. Lala tells Risa and Mio about Saruyama becoming a gift for the wolf, and so they decide to dress him up as a fish so he'll look like a more memorable souvenir. They take Saruyama to the wolf to show her that he's ready to be taken with her. The wolf then asks if Saruyama is going out with another girl, because if he is, she believes his happiness is important and doesn't wish to interfere with his relationship. Lala says he isn't, but Saruyama quickly declines and takes advantage of this moment to find a girl quickly as an excuse to not be taken as a souvenir. All the girls in the school reject him however, except for Haruna who tries to help him. As Saruyama asks Haruna to go out with him, Rito becomes jealous and stops Saruyama from using Haruna. Now incredibly deperate for an excuse, Saruyama finds a dog outside which he uses as his excuse. As he goes back to the infirmary to show the wolf mother his newly acquired girlfriend, Lala tells them that she left with her baby because she wants Saruyama to be happy. Saruyama cries from hearing this, and then discovers the dog he found was actually a male.

Lala is seen watching a commercial on tv about the Tsumata Misami Hot Springs. She then tells Rito that she wants her own hot spring. Rito finds Lala attempting to build something in their yard. Lala then asks Rito to go get her a drink, so Rito heads to the store where he is suddenly attacked by Yami-chan as a test. Rito tells her that Lala is back at home building something, in which after hearing this, Yami-chan leaves. When Rito returns, he finds that Lala constructed a large drill machine which she intends to use to dig underground and hopefully find a hot spring. Mio, Risa, Mikado-sensei, Yami-chan, Haruna-chan, and Saruyama are all invited to join Rito and Lala dig underground. As they travel, they find Tokugawa's hidden treasure and the entrance to Atlantis, which Lala blatantly passes by due to there being no presence of a hot spring nearby. They eventually come across what is called the Seven Colored Hot Springs due to the water appearing as seven different colors. All the girls enjoy using the big and spacious springs, while Saruyama and Rito are stuck using a very small and cramped one. Saruyama decides to get out of the small spring and mess with the girls in the other hot springs. Rito soon follows, and sees Saruyama chasing after Risa and Mio, which Rito then tells him to stop. They come across Mikado-sensei and Yami-chan, who then punches them both with her hair stating that she hates ecchi people. Lala then tells Haruna she needs to leave the spring to try and find a hot spring she can bring back to Rito's house. Rito then finds Haruna and they try to start a conversation with each other, which is then interrupted by Lala who tells them that they need to leave quickly because she accidentally hit an underground volcano. They come across a civilization of moles who seek to rule the Earth's surface, but the moles are then killed by the flowing magma, and everyone returns safely to the surface.

It is a filler which features a Magical Kyoko-kun episode. Kyoto must protect the city from the evil General Mojack. General Mojack is trying to take over Earth by turning everyone's hair into an afro. Rito and Lala make a very short appearance at the end of the episode, which shows that both of them are just watching the Magical Kyoko-kun tv show. Lala is very excited about the show, but Rito is bored.

Tempted at the prospect of running Earth’s only (and potentially the universe’s best) alien hotel by Mikado-sensei and Galaxy Network’s editor, Kimio, Rito decides to give it a try using the old school building. After Lala calls upon Zastin and her other bodyguards to help rebuild the dilapidated building, the Yuuki Pavilion opens and begins accepting customers. While the number of customers increases, Rito finds himself overrun and is quickly becoming exhausted; as a result he begins to recruit help from Oshizu, the ghost inhabiting the building, Yami-chan, who works as a maid in order to stay for free, and his sister Mikan who will be the chef for the inn. As the number of customers eventually dwindles to zero, a large group of miniature samurai-like men, from the planet Ako, begin to arrive. During repeated attempts to solidify an attack plan on the planet Deviluke, they are repeatedly interrupted by Rito's attempts to offer them food and a bath. Eventually the leader accepts an offer of tea while he is in the midst of using a hologram to show the systems outlying Deviluke. When one of his men tries to hide the hologram, he responds by saying, "Don't mind it. The primitive people of Earth won't understand what it is." Lala, however, immediately recognizes the planet on display which leads to a confrontation between the samurai and Rito, Lala, Yumi-chan, Zastin and the bodyguards. In the end, the inn is destroyed and with it Rito's dreams of being the universe's best alien hotel are lost.

After reflecting on her experiences on Earth, Yami reminds herself that she’s an assassin and decides to look for a job. At school, Yui tries to coordinate what her class is going to do for the culture festival and gives only two options, a calligraphy display or a region research exhibit, much to everyone’s disappointment. Saruyama takes the lead and the class chooses to take on an animal cafe for their project. The class prepares for Culture Day as Yami continues to look for work in assassination however, when she fails to find employment, she returns to the school in time to help with the animal cafe.

After watching Rito and all the girls around him, Saruyama becomes jealous of his popularity and wishes he was a noble in Edo Castle. He then has daydreams of his many adventures as the ruler of Edo Castle, where all his friends make appearances.

Lala starts acting weird one morning, and is diagnosed with a fever that causes her to change personality every day. Rito has to deal with a new personality each day while waiting for her medicine to arrive, and has to thwart a plan to take over the world constructed by a harsh, dictator-like deviluke princess.

After taking back his daughter, the King of Deviluke sends Zastin to deliver a message to Rito. Rito finds out that, the next day, he needs to board the Devilukian spaceship to prove he is really number one in the universe. He confesses his feelings to Haruna, and takes off the next day to board the spaceship, with the citizens of Japan, and Earth, cheering for him. Eventually, he comes across a dangerous plant that grows extremely fast. he manages to run away, but cannot do so forever and gets caught. However, a SUV comes and Kotegawa saves Rito, only to hit him again for a misunderstanding. Mikado drives the SUV towards the spaceship and the episode is left at a cliffhanger.

Starting where the last episode left off, Rito is still trying to make it to the ship in time. With more challenges, he starts to lose hope and eventually goes into a dream of him, Haruna, and Lala. After awakening to Haruna and Lala yelling, he makes it to the ship. Then it cuts to a marriage where Lala says she can't marry him unless he wants to. Using her memory erasing tool, she then tries to start a new life on Earth, but ends up just transferring back into the school because her invention, like many others, is faulty, and a new adventure then begins.