Yume Nijino and her friend Koharu Nanakura, who want to join the top idol group S4, enroll at the idol school Yotsuboshi Academy, where the four members of S4; Hime Shiratori, Yozora Kasumi, Yuzu Nikaidou, and Tsubasa Kisaragi, study.

As word spreads about Yume's performance, despite Yume herself being unable to remember what happened or repeat any of the prowess she showed in class, she and Koharu check out the various classes they can audition for.

With the class sorting auditions approaching, Yume worries that she isn't good enough to join the Song Class.

The first year students in the Song Class are tasked with working backstage at Aikatsu TV, setting up a stage for a fashion show that Hime and Yozora are appearing in.

The students are tasked with using the Dress Make system to design their own dresses.

Yume, Koharu, and Rola decide to enter an audition for a drama starring S4, despite none of them having acted before.

Rola enters an audition searching for individualistic idols to be the mascot of an ice-cream company.

As a fashion model contest is held for the Beauty Class first-years, Koharu befriends her classmate, Mahiru Kasumi. Koharu becomes hesitant to enter the audition, feeling she is lacking compared to everyone else, but Yume and Rola encourage her to have more confidence in herself.

Yume and Rola are selected to represent Yotsuboshi Academy in an open audition for a confectionary campaign girl, competing against idols from other schools.

Yume is requested by the school's headmaster, Hikaru Moroboshi, to hold her first solo concert after Hime's concert gets cancelled.

As an apology for the trouble caused by her concert's cancellation, Hime offers Yume the chance to be her manager for the day, as a television crew documents her schedule.

Following a performance together, Yume and Rola encounter a scary creature on their way back to their dorms, where they face a punishment from Tsubasa for being late.

Yotsuboshi Academy puts on an original movie in which Yume stars as a small fairy. Learning that her sister, played by Hime, has been kidnapped by a demon lord, Yume goes off towards his castle, coming across various allies along the way including M4's Nozomu.

Yozora announces a contest for students to design their own dress for Romance Kiss and wear it in a special performance. While exploring town for ideas, Yume, Rola, and Koharu come across both Yozora and M4's Asahi, who are both revealed to be Mahiru's siblings.

As the top scorers of their respective classes, Rola, Ako, and Mahiru, along with the Dance Class' Luka Haruka, are chosen to pair up with the S4 members and compete in a Summer Fest tournament with lunch coupons up for grabs.

While out doing a commercial shoot on the morning of the second day of Summer Fest, a camera malfunction puts Rola at risk of not making it back in time for her performance with Hime.

Yume, Koharu, Rola, and Ako appear on M4's variety show. As Ako remains intent on getting Subaru's attention, she is warned by Kanata Hira to keep things under control and treat her fellow idols as equals whilst on air.

The girls hear about the Fresh Idol Election, in which the first-year idols will be ranked by fan votes, with the top four idols appearing in the upcoming Aikatsu Island event.

Hoping to help Koharu with her heat exhaustion, Yuzu invites the girls to a Dance Battle tournament that she is participating in.

Yume and the others sneak onto the set of a movie that Tsubasa is starring in alongside the rest of S4. During the shoot, Tsubasa gets a lot of slack from the lead actor, Taiyou, who seems to have lost his passion for acting.

As the Song Class are faced with an audition to make their CD debut, putting Yume and Rola is direct competition with each other, they are required to wear weighted clothing during their training.

Due to Moroboshi's meddling, Yume is given only a short amount of time to record a mini-album for her debut CD, with Hime's new album planned for release on the same day.

Wanting to find her own individuality, Yume and the others go searching for seven "luckies" around the school said to grant wishes.

After giving a group performance, Yume, Rola, Mahiru, and Ako are given a three day break from their activities. Learning that Yume's family runs a well known bakery, the girls all go to Yume's house to try their pastries.

As students are given roles in a Broadway Dream production for the upcoming school festival, Koharu is selected as a show dancer for one of the musical numbers.

Lily returns to Yotsuboshi Academy, though still struggles to participate in activities due to her weak constitution.

Yume and Lily go with Hime to her dress brand, My Little Heart, to observe the completion of her new dress.

On Halloween, the students are tasked with gathering the most candy through trick-or-treating in order to be crowned the Halloween Princess.

As the girls take part in an audition to perform during a soccer half-time show, Koharu is conflicted about potentially having to relocate to Italy with her family.

After hearing from Koharu that she is moving overseas in a week's time, Yume works with her friends to throw her a surprise farewell party.

With students tasked with forming three-girl units for the upcoming Autumn Festival, Tsubasa invites Mahiru to join her unit alongside Yozora, which they decide to name Sky-Girl.

Roped into joining Yuzu and Ako's unit, Yuzukoshou, Yume is unable to get into the swing of things as she is worried about what would happen if she fails again.

Noticing Rola is still in a funk over not being able to beat Yume, Anna and Moroboshi arrange for her to be sent with Lily to the Spa Resort Okunotani.

As Mahiru is offered her own regular feature in a fashion magazine, she comes across two rude ganguro high school girls, Motoko and Eiko, scolding them for littering.

Still worried about her power kicking in, Yume asks Hime for a full explanation about what is happening to her.

Moroboshi arranges for Yume to hold a solo concert, threatening to expel her if she cannot satisfy 90% of the audience.

The admins prepare to hold a party for Christmas Eve with a stream of S4's concert, encouraging Yume to put on a performance of her own alongside Rola, Mahiru, and Ako.

After hosting a New Year's show, the S4 girls look back on how Yume and the others have grown over the past year, contemplating who is likely to be chosen for the upcoming S4 Selection.

Overhearing a conversation between Moroboshi and Anna about the school being in financial crisis, Lily offers to represent Yottsuboshi Academy in a Russian brand designer contest which is offering a sponsorship for the winner.

The girls star in yet another drama, titled Aikatsu Detectives! The Princess Diamond Incident. As phantom thieves known as the Shadow Stars plot to steal Hime's Princess Diamond, Ako joins Tsubasa, Yuzu, Yozora, and Mahiru as part of an investigation team guarding the diamond at a party.

The school holds the Star Catching Festival, in which each class must use their talents to win different areas by earning votes from the townsfolk.

Yume is requested to appear on The Best of Music Show's Valentine's Day Special alongside M4, receiving some pointers from Subaru on how she needs to convey her feelings to the audience.

As both Rola and Mahiru become worried about whether they've progressed, Mahiru takes Yozora's advice to perform more and decides to put on a special event with Rola.

Wanting to get her own Grade Up Glitter to catch up with the others, Ako searches for a venue for her own performance.

The S4 Selection begins, with Yuzu retaining her spot at the top of the Dance Class. Preparing for the Theater Class selection taking place the next day, Ako becomes determined to outperform Tsubasa and take the top position.

Mahiru prepares to face off against Yozora in the Beauty Class' selection. After both sisters bring out their all in their performances, Mahiru wins the top spot by a small margin.

The time finally comes for the Song Class selection, with Yume, Rola, Lily, and Hime all competing against each other.

Just before her performance, Yume gets a call from Koharu, giving her thanks for everything she has done for her.

With the crowning ceremony, Hime, Tsubasa, and Yozora officially announce Yume, Ako, and Mahiru as their respective successors, joining Yuzu in S4.