Ritsu Tainaka wants to reform the light music club which will be disbanded by the end of April if at least four members cannot be found. They put up a poster for the club which catches the eye of Yui and she submits a form to join the club. The three members perform a short piece for Yui; this inspires Yui to finally join the club as a guitarist, though she first not only has to buy one, but learn how to play it first.

The members of the new light music club join forces in order to get Yui Hirasawa a guitar, an expensive Gibson Les Paul which costs ¥250,000.

Yui and the girls are now taking their midterms. Unfortunately, Yui practices playing her guitar chords instead of studying, and she fails the exams. If she fails the retake exams, she cannot participate in club activities, and the club will be disbanded. A day before the retake, Yui still has not been able to study much and begs Ritsu, Mio and Tsumugi into helping her to study for her retake. Days after the retake, an exhausted Yui returns to the club room with full marks. To celebrate, the girls ask Yui to play the guitar chords she had learned, but she has completely forgotten them.

After listening to the live performance of the previous year's Light Music Club, Mio is inspired to get the gang together to practice over the summer break for the upcoming Budokan school festival. They travel to Tsumugi's oceanside villa, where music and summer fun mix.

When Tsumugi's application to reserve the hall for the light music club is rejected due to it not officially being a club, it becomes apparent Ritsu had forgotten to fill out the required form. Yui's friend Nodoka Manabe, who is a member of the student council, offers to register them, but says they will need an advisor. The girls ask one of the teachers, Sawako Yamanaka, who rejects the offer until Yui figures out she was one of the previous light music club members, and Ritsu plans to blackmail her with the information.

On the day of the school festival, Mio wants to practice for the club's live event, but everyone else is helping with their classes' other stands. They later get some practice done, but Mio is still nervous about singing center stage, even with Sawako's costume choices not helping the matter. Ritsu decides to hold a mock concert introduction to calm her nerves, although she still has jitters when the concert starts. Having seen her secret vocal practice beforehand, the others encourage her to do her best and the show manages to be a success. However, leaving the stage Mio trips over the guitar cable and accidentally exposes her underwear to the audience. She ends up getting a fan club, but cannot get over her embarrassment.

Ui remembers how Yui once attempted to give her a white Christmas by sticking pillow stuffing on the tree outside. Ritsu decides to hold a Christmas party for the club, and while her initial plans of holding it at Tsumugi's house fail, they eventually decide to have it at Yui's house, also inviting her friend, Nodoka Manabe. They also decide to do a gift exchange, and go shopping for various gifts. Ui prepares a lovely Christmas dinner for the group, which gets a little out of hand when Sawako shows up out of no where. During the gift exchange, Yui and Ui give each other some warm things for the winter. After the rest of the group leaves, snow falls and Yui and Ui decide to sleep together, although Yui ends up hogging the sheets. In the New Year, the club decides to go to the shrine to make their New Year wishes.

Ui makes it into Yui's school as a freshman, as well as new student Azusa Nakano. When the class arrangements are announced, Yui, Mugi and Ritsu end up in the same class, whilst Mio ends up in a different class with Nodoka. The group put up with Sawako's ideas of promoting the club by dressing them up as animals. Ui and her friend visit the club only to find everyone dressed as maids. However, the band find it impossible to play with the outfits on. Meanwhile Azusa walks around looking for a club that's right for her. The group gets ready for a live performance, but Mio is too embarrassed to do the vocals, so Yui does them instead. Yui forgets the lyrics, but Mio manages to back her up. Ui brings Azusa to watch the show, who is so moved by it that she goes to join the club.

Azusa officially joins the club, although is shocked to find everyone drinking tea and eating cake instead of practicing. She yells at them when Sawako tells her off for actually practicing, but Yui manages to calm her down. Despite her objections, Azusa finds herself weak against Tsumugi's tea and cakes. Yui herself is rather shocked at how much better Azusa is at guitar than she is. Sawako brings a pair of cat ears for Azusa to wear, leading Yui to give her the name 'Azu-nyan'. Noticing she is a bit upset, Mio encourages the band to practice more, but the group quickly reverts to its lazy state. Azusa becomes really upset since she cannot understand why the band members she admired at the live performance behaves like they do. Mio explains to her that she stayed with the band because it is fun to play with the others, and Azusa decides to stay as well.

Azusa meets up with Ui for lunch and are later joined by Ritsu. They try to call Tsumugi but end up talking to her butler. Yui and Ritsu invite Sawako to join their next training camp, but she appears disinterested. The gang arrive at an even bigger villa than last year, though Mugi points out it still isn't the one she desired. Yui and Ritsu want to play and Mio and Azusa want to practise, but the latter gets outvoted by Tsumugi in favour of playing. Azusa objects, but ends up having the most fun anyway, even getting sunburnt in the process. After practise, dinner and fireworks, Ritsu suggests a test of courage, and Mio and Azusa are shocked by the sudden appearance of Sawako. Later that night, Azusa joins Yui practising guitar. Azusa meets up with Ui again, although she can barely recognise her with all the sunburn.

When Ritsu is reminded by Nodoka to fill in her gym-use application, the band notice they don't have a name yet. Azusa notices rust on Yui's guitar strings, and it becomes apparent that Yui has never given her guitar maintenance before. They take it to the guitar shop where Mio gets entranced by a Lefty fair. However, Yui doesn't realise she has to pay for maintenance, and when Tsumugi tries to pay, the staff refuse to take money from her. They tell her to consider it as a free service. Later, Ritsu starts to become jealous of Mio spending time with Nodoka and begins to fall out with her. She ends up with a fever, so Mio visits and smoothes things over. Afterwards, Ritsu gets in trouble for still forgetting her form, but Nodoka backs her up. Since none of the members could decide on a name for the band, Sawako chooses the name "After School Tea Time" to get it over with. However, Yui ends up catching Ritsu's cold.

Yui is still sick from her cold, which is possibly attributed to her wearing a short yukata for too long. As the band tries to make do with Azusa as lead guitarist, Yui supposedly shows up over with her cold. However, her playing is too perfect and a slip of the tongue reveals that she is actually Ui, who had managed to play after a few days practice. Yui appears, but is still in no condition to play, so Mio suggests that she stay home until the day of the live performance. Yui eventually makes it in time, but forgets her guitar at home, so Sawako fills in for her while she goes to get it. Yui returns in time for the second song and the performance goes well, and the band even does an encore.

As the cold winter weather creeps in, and despite Yui's offer of having nabe with everyone, each of the club members have individual duties. Tsumugi gets a part time job at a fast food restaurant, Mio goes to the beach to get inspiration for her lyrics, Ritsu has to entertain her little brother and Azusa is asked to look after her classmate's pet cat, despite not being good with cats herself. However, Mio cannot think of anything to write, Tsumugi buckles under the pressure, Ritsu ends up by herself and Azusa is left uncertain what to do when the cat starts throwing up. A random text from Yui cheers up the others and she comes to help Azusa with the cat. They all meet up for burgers where Ritsu is shocked to find what she thought was a love letter addressed to her was actually a set of lyrics Mio wrote.

Afternoon Tea Time plays their first show at a club.