Kin-iro Mosaic: Pretty Days is an OVA released November 12, 2016 in theaters, and March 3, 2017 for DVD. It takes place after Season 2.
While preparing for their play during the upcoming Cultural Festival, Aya feels distanced from Shinobu due to not having any shared memories with her from elementary school. As everything is being put together, she recalls their time preparing for their High School entrance exams and the hard decision she was soon forced to make.
The movie begins with a flashback to when Aya first met Shinobu and Yoko, after she is introduced to the class. Aya was very lonely and shy, but Shinobu wished to make friends with here immediately, and so strikes up a conversation in the hallway. It then cuts back to the present, where Shinobu is musing about how she struggles to get up in the mornings. Despite this, she has been dedicated to working on a play for the school festival. Yoko casually mentions how she used to give wake-up calls to Shinobu in primary school, which causes Aya to begin to worry if she is not as important a friend to Shinobu since they did not meet until middle school.
After class, Karen announces that she will be playing a lead role in Shinobu's play, and Yoko jokes about wanting to see Aya in the play. Once again Yoko mentions how Shinobu was in primary school, which causes Aya to be more upset. A little later, Aya walks past the room where Shinobu is designing clothes, and this time also observes Shinobu's love for blonde hair. Aya then gives a mental monologue about how she has not been friends with Shinobu for as long as Yoko, and does not have blonde hair like Alice and Karen. As such, she fears that Shinobu sees them as more important friends than her. The girls notice Aya at the door, but think little of it, except for Yoko who can tell right away that something is troubling her.
Later at Shinobu's house, Aya is still feeling a little down. While helping Shinobu work on the play, Shinobu abruptly announces that she and Isami must go to the store. Yoko then notices that Aya is still down, and at the same time, Karen asks how Shinobu got into the same high school as Aya. This prompts Yoko to begin telling the story, and Aya listens while continuing to sew.
We see Yoko's story in a flashback scene. The three girls are in middle school, and Yoko and Shinobu are concerned that their grades may not be good enough to get into the high school that they want. They discuss what high schools they might choose to go to, and Aya mentions her interest in going to a prestigious school called "Suiren Girls' Academy", however Aya also subtly hints that she does not necessarily want to go there, as it is far away, which will separate her from Shinobu and Yoko. Aya also mentions a nearby school, which is the school they go to in the present, and Yoko and Shinobu immediately fall in love with the school and the uniform. After being shown around the school by Karasuma Sensei, they both decide they want to go to the school, however Yoko brings up the problem of their grades. This prompts them to ask Aya to teach them and help them study. Excited by the prospect of helping her friends, Aya agrees.
They meet at Shinobu's house, and right away Shinobu and Yoko are having difficulty with the topics. Aya also notices a picture of Shinobu and Yoko in primary school together. The next day they meet at Yoko's house to study, and in a familiar scene Aya is nervous about visiting Yoko's house for the first time. Aya mentions that Suiren Academy is her first choice of high school, which seems to upset Shinobu a little as she knows they'll be separated if Aya goes there. Yoko expresses concern that in helping her and Shinobu, Aya may not be getting enough time to study herself, but Aya assures her that she studies in her own time.
After a practise test, Aya notes that Yoko is making progress, but Shinobu is still struggling. She is disheartened by this, but Aya and Yoko assure her that she still has time to improve. Shortly after this, Shinobu begins to increase her studying time, and starts making faster progress. Impressed, Aya tells her she will ramp up the difficulty to ensure Shinobu does well on the entrance exams. They continue to study together after this for the next few days.
Aya takes the entrance exam to Suiren Academy (which takes place at an earlier date), and on results day learns that she has been offered a place at the school. Yoko and Shinobu congratulate her, but Aya does not seem to be as happy as she should be. Over the next couple of days Shinobu continues to study hard, and the movie cuts forward to the day of her exam. Karasuma Sensei sees them enter the building and wishes them luck. On their way to the exam room, they pass Aya who is wearing a disguise, however, after a couple of seconds Yoko recognises her. She reveals that she is taking the entrance exam to this school too. After the exam, Yoko and Shinobu are concerned as they found the tests difficult, but Aya cheers them up, and it is implied that she is confident that they have passed, although she does not state it explicitly.
On results day, Aya is relieved to see that she had also passed this entrance exam, but Yoko and Shinobu are too nervous to check, and so ask Aya to check for them. After checking the board, Aya tells them to see it for themselves, and they see that they have both passed. All three of them celebrate. Later, Aya is trying on a Suiren Academy uniform, but appears very upset, and decides she would prefer to join the same school as Yoko and Shinobu. She tries to tell them this, but Yoko tells her she doesn't have to say anything, as she believes Aya will tell them how she will miss them at her new school. When Aya shows up at their school on the first day, they are therefore pleasantly surprised to see her there, and she explains that she changed her mind about her first choice school.
Yoko's story ends as the movie cuts back to the present day, and both Alice and Karen are very impressed with what Aya had done for them. Yoko thanks Aya for everything she did to help them, which embarrasses her. Shinobu arrives back from the shops, and states she has gotten a present for everyone. She tells them to close their eyes, but hands them nothing, and explains that she could not think of something that everyone would like, and so the present is the bond of friendship. Alice and Karen are understandably disappointed, however Aya feels re-assured by this, and the story, and begins to realize that she is also a very important friend to Shinobu.
It is the day of the play, however the girl who was going to play the princess is ill and cannot perform. Shinobu asks Aya to take her place, but she is initially too nervous to do so. After some convincing, she agrees, but continues to feel very nervous as she walks on stage, until she sees Yoko and Alice cheer her on. When it is Karen's turn to be introduced, however, she has forgotten her lines, and begins improvising. This confuses Aya, but Shinobu is determined to make the play work, and so has Karasuma Sensei, Alice and Yoko join in, and the play becomes a success. At the end of the play, Aya whispers to Shinobu that she is really happy she chooses to come to the same school as her. The movie ends with Shinobu smiling back, and a post-credits scene shows the girls' first day at the high school, where their friendship with one another is shown to be very strong.