The plot begins after K-On!! episode 22. After they are accepted by the same university, Yui, Ritsu, Mio and Tsumugi try to figure out a present to give to Azusa before they graduate, and they all decide to go to London for their graduation trip. Upon arriving, they end up having to give a performance at a sushi restaurant after being mistaken for Ritsu's friend's band, Love Crisis. As the girls enjoy the sights, Azusa seems to be rather cautious around Yui's odd behavior, having almost walked in on their plans before. Later, the girls are asked to do a performance for a Japanese Pop Culture Fair, where they are soon joined by Sawako, before they catch their flight back to Japan. Upon returning home, the girls perform a special live concert in their classroom. Afterwards, Yui, Ritsu, Mio and Tsumugi work in secret to prepare a special song for Azusa, which they present to her on the day of their graduation at the end of K-On!! episode 24.

Shortly before episode 14, after receiving souvenirs from Tsumugi's trip to Finland following the summer festival, the girls decide to plan for an overseas trip after graduation. They practice various things for overseas travel, only to realize that, besides Tsumugi, none of them has a valid passport. While lining up to hand in their passport applications, Ritsu realizes she forgot her identity card so she sends her little brother Satoshi to fetch it. Mio needs to take a suitable photograph to complete her application, but keeps getting bothered by the others while attempting to take it. With everyone having their own ideas of where they would like to go, Yui suggests that they go on a second trip after Azusa graduates.

Yui takes the role of a superhero and helps the girls with other tasks. At the end, the other girls wish Azusa luck with running the High School Light Music Club.

Tsumugi and Ui retell fables with Yui and Azusa acting as some of the characters.

After the school play, Yui comes up with ideas for musical adaptations of their songs.

Tsumugi acts as hostess to a cooking program as two of the girls and Sawako show off their meals.

The girls have a contest to see who is the best MC.

The girls look over the dreams they had when they were younger.

Since Yui and Ritsu have siblings, the other girls wonder what kind of siblings they would have.

The senior year girls talk about the souvenirs they bought during their school trip to Kyoto.

Azusa becomes a fortune teller, learning everyone's dreams in order to tell them about their former lives, which happen to be of various bugs.