It's Seiya's birthday and Isuzu plans to give him a birthday gift. However, a series of events that unfolds keeps thwarting her plans.
Isuzu Sento forces Seiya Kanie, at gun point, to go on a date with her. The location turns out to be Amagi Brilliant Park. While roaming around the place, Isuzu introduces Seiya to the various attractions, and it is very apparent that all of them are very unsatisfactory. After going once over the Park, Isuzu asks Seiya to his thoughts about the place, to which he responds very negatively, finally spouting "You need to believe in a dream yourself for other people to believe in it!". Just when he's about to leave, Isuzu offers him some croquettes, which turn out to be very delicious. Deciding to know who made them, Seiya follows Isuzu to meet the manager of the Park, Latifah Fullanza. She describes that the Park actors are actually residents from a Magical land, and if they are not able to get enough customers in a determined time, the park will be shut down, and asks Seiya to help by taking over the manager position. She also tells him that she will give him magical powers.
The next day, Seiya realizes he has the power to read people's mind. Isuzu again takes him to the park, where they proceed to meet some people from Amagi Development - they are the ones who would take over the Park once the time expires. One of them recognized Seiya and tells him not to get close to the losers in the Park, or he too will become one. In the Park, an assembly is held, where the Princess, Latifah Fullanza announces that the Park will be closed in three months. Seiya returns to them and announces that he will save them. But later, when he's alone with Isuzu and Latifah, he says that he just claimed it to raise everyone's spirit, but he's not actually confident about it - but Latifah claims having complete faith in him.
Seiya makes an announcement for cast workers saying that park will be closed for a day due to repairing. Then he declares three changes: the park will close at 7 p.m., cancel Friday's day-off and set up a 30 yen payment for all services. When Moffle hits an annoying guest, Isuzu shoots the guest and his family with bullets which causes memory loss. Salama records the fight with her cell phone. Seiya records a promotional video with the Elementario fairies, Latifa and Isuzu wearing swimsuits, but it does not get as many views as expected. Then he uploads an edited video of the fight, which gets many hits, and as a result gave many views to the PV uploaded beforehand.
Thanks to Seiya's flawless management, the park's efficiency and visitor count is increasing, and when informed by Sento that Moffle, Macaron and Tirami have some complains, he decides to let her deal with them instead, but the Elementario Faeries show him that instead of looking for a compromise, Sento just ends the discussion by threatening them with her gun. Seiya then scolds Sento for her behavior, creating a divide between them. In the next day, Latifah asks Seiya to ride the ferris wheel with her and in the occasion, it is revealed that he has a fear of heights, and when conforted by her, Seiya has the feeling that they have met before. Some time later, it starts raining, and with the drainage system broken, threatening to flood the entire park, Sento takes the lead and organizes an emergency operation to prevent further damage. After the rain, Sento reveals that her strict behavior to others is thanks to her military training, and believes that everyone in the park hates her because of that, but Seiya shows her the happy faces of the cast who thank her for her help, proving her wrong.
The Amagi Brilliant Park has used all its savings and there is no money left to keep it running. However, Moffle remembers about their friend Dornel, who got missing after searching for treasure in an abandoned area of the park, and Seiya, Isuzu, Macaron, Tiramy and Moffle leave to investigate. While facing several traps along the way, Isuzu and Macaron get separated from the others and discover that Dornel was hidden inside the cave all this time, indulging on several hobbies, while Seiya and the others confront Rubrum, the Red Dragon, and learn that Rubrum and the Diggeries, a group of mole-like fairies were running away from a tyrannical empire and given shelter in the park. Back to the surface, Rubrum and the Diggeries ask for a job in the park as well, and Seiya agrees, while all the items Dornel gathered during his absence are sold to pay for the park's expenses.
With the park short on staff, Seiya decides to hold a job interview for new workers and Isuzu gets herself in serious trouble when she unwillingly eats a fruit that forces her to always tell her mind, leaving her in fear of revealing her true feelings for him.
The park is on alert when a group of pirates from Maple Land appear to wreak havoc. With Isusu, Latifah, Moffle, Macaron and the Elementario Fairies in their custody, it's up to Seiya and the others to make a stand against the pirates and rescue them. All of that without having the guests realize that it is not an act.
Seiya gets a summer cold but he can't afford to skip school due to his earlier absences. Sento, Macaron, Tiramie and Moffle wear a realistic suit of his body one person per day and attend school in his stead. On the first day, Isuzu finds a love letter in Kanie's shoe locker but the sender, Tsuchida Kanae, had only mixed up his locker with someone else. As Sento tells her inspiring words, Kanae ends up developing feelings for Kanie instead. The next two days end up with disgusting incidents due to the mascots' behavior, while the forth day ends peacefully due to Kanie wearing a suit of a boy to whom Kanae had tried to send the letter originally, Kimura, and lying that all the disgusting acts from 'Kanie' the days before were meant to drive Kanae back to Kimura by making her hate Kanie.
Having not improved at all with their attraction due to their lack of teamwork, the Elementario Fairies are invited for dinner with Latifah and unwittingly activate the castle's defense system. Trapped inside the castle, the fairies must reinitialize the system from the inside, but to do so, they must pass a series of trials that demand them to work together.
Everyone's doing their best but it seems impossible to reach the goal of 250.000 visitors. Isuzu tells Kanie why Latifah faints so often. It turns out that there's a Animus-draining curse upon the princess. Amagi Brilliant Park was built to keep Latifah alive. Seiya recalled the meeting with the princess when he was young, but she looked exactly the same then. Moffle told him that the curse not only affects her health, but also resets her memories and physical development every year. With only 10 days left to the deadline, Seiya hears from Triken that he found what he asked him to look for, renewing his hopes.
Seiya's plan to reach the quota in 10 days involves hosting a soccer match at the park's stadium. After convincing the local soccer team to play an important match at the park, Seiya informs the cast that for their plan to work, a large unused area of the park grounds must be sold in order to pay for the expenses and solve their financial problems, to which they agree, and then they spend the following days making preparations for the match, while Seiya is still worried, knowing that on the last day, Latifah's memories will be reset and she will forget about him at all once more. The final day comes at last, and with all the visitors counted and a few hours left to the deadline, Seiya gets in shock upon knowing that they are only 252 visitors short from reaching the goal.
As a last resort, the staff of Amagi Brilliant Park invite all their friends and relatives, reaching the quota in the nick of time. Announcing that it's his last day as manager, Seiya reveals to the others that a huge shopping mall will be established in the land he previously sold, which will help bring guests to the park. Takaya Kurisu from the Amagi Development, compliments Seiya for the feat, but also mocks him because the issue with Latifah's condition is yet to be solved, revealing himself as the wizard who cursed her in the first place before fleeing. However, when midnight comes, Seiya and the others discover that the huge quantity of Animus gathered in the last weeks was strong enough to break her free for the curse, much to everyone's joy. Seiya then bids farewell to the people of the park, but when he returns home, his aunt Aisu Kyūbu remarks how happy he was while working there, thus in the next day, Seiya returns and reassumes his post as the manager of Amagi Brilliant Park, claiming that there is still a lot for him to do.