故事发生在樱丘高中，围绕着由五个成员组成的轻音部展开。这支名为“放学后茶会”的乐队中，担任吉他和主唱的是天然呆少女平沢唯（丰崎爱生 配音），担任贝斯手的是稳重但容易害羞的秋山澪（日笠阳子 配音），担任鼓手的部长，是非常有活力的田井中律（佐藤聪美 配音），温柔热情的键盘手是琴吹紬（寿美菜子 配音），吉他手是学妹中野梓（竹达彩奈 配音）。新学年开始，除了小梓，大家都升上三年级，还被分到了同一个班级。然而要是再不招揽新成员入部，来年四名成员毕业离校，轻音部就要面临废部的命运了。
新学期樱高的各大社团都开始紧锣密鼓地招新，轻音部也使尽了各种办法，她们在新生欢迎会上的演出，能否吸引新人加入呢？K-ON!的青春故事在第二季中继续进行！

Devoted to her family’s rice-cake–making business and the high school baton club, Tamako is a little slow when it comes to love. She’s oblivious to her childhood friend Mochizo’s affections, even though all their friends know. With graduation closing in and Mochizo leaving for Tokyo, will Tamako realise her feelings and tell him in time?

坐落于某个小镇的兔山商店街（うさぎ山商店街）上，有个经营饼店的少女－－北白川玉子。除了帮忙店里的事情，她亦有跟学校的朋友常盘绿和牧野神奈参与舞棒部活动。而饼店对面的大路家是同一行业的竞争对手，两边的父亲经常都因生意问题而喧闹一番。然而大路家的儿子大路饼藏却是玉子的朋友，但玉子从没注意到饼藏的好感。总而言之，玉子在商店街众人的护荫下，热闹地度过每一天，生活可谓过得相当快乐。

除夕，也就是玉子的生日，处于商店街年末最繁忙的时刻。庆祝仪式已是商店街上下的惯例，唯独饼藏今年没有准时来到。直到他带着礼物来到之时……

商店街突然出现了一只懂得说人话的鸟，犹如飞车般降临到众人面前。偶然变得越来越热闹的兔山商店街，亦正式开始其稍微不同的新一年。

Yuuta and Rikka are in their third year of high school. One day in Spring, Touka declares that she will take Rikka to Italy with her, as her job has stabilized there and thinks they should migrate together as a family. Touka is also worried about Rikka not being competent enough to advance to universities in Japan. The gangs from the club suggested Yuuta, who doesn't want to be separated, to elope with Rikka!! A runaway drama throughout Japan begins.

Yuta Togashi has a problem. He used to be a "chunibyo," one of the thousands of Japanese students so desperate to stand out that they've literally convinced themselves that they have secret knowledge and hidden powers. But now that he's starting high school, he's determined to put aside his delusions and face life head on. The trouble is Rikka Takanashi, his upstairs neighbor, is just a little bit delusional herself. And she knows all about his past indiscretions.

樱丘高中的新学期开始了，这不仅仅意味着有许多新的面孔将出现在校园里，同时也意味着，一场轰轰烈烈的社团招募大战即将拉开帷幕。天然呆少女平泽唯（丰崎爱生 配音）对新的校园生活有着一份憧憬但也心怀忐忑，这时一个大大咧咧的女孩田井中律（佐藤聪美 配音）出现在了她的面前。在阿律的热情邀请下，有些迟钝的小唯莫名其妙的成为了“轻音部”的吉他手。来到轻音部活动室的小唯见到了贝斯手秋山澪（日笠阳子 配音），这个有些正经但又有些害羞的黑长直让小唯心生好感。但这时小唯才发现，这个传说中的轻音部，所有的社团居然就是她们三人，而按照学校的规定，凡是不满四人的社团就要被解散。怎么办？刚刚加入社团的小唯，立刻要开始为了保证社团不被解散而开始奋斗！