Yui Hirasawa (平沢 唯, Hirasawa Yui)
Voiced by: Aki Toyosaki
Yui is the main character of K-On!. She is one of the members of the light music club, and plays a Heritage Cherry Sunburst Gibson Les Paul Classic electric guitar that she nicknames 'Giita' (ギー太?). She does not get good grades in school (though when properly coached, she can achieve astounding results) and is easily distracted by trivialities. Yui is clumsy and easily spaces out most of the time. She takes a huge liking for any kind of food (but admits that she does not gain any weight). She has her younger sister Ui to take care of her and keep herself in line. She has a very easy-going nature, but has incredible concentration when hyped, though this is only limited to one subject at a time. She will totally neglect any other things in the process, to the point of forgetting anything she has learned beforehand. Despite all of this, Yui is still devoted to her band and will practice hard enough for the club. She has perfect pitch and is one of the group's vocalists, although she is known to forget her lyrics in mid-performance, as well as overdoing things, making her unable to perform sometimes.
Ritsu Tainaka (田井中 律, Tainaka Ritsu)
Voiced by: Satomi Satō
Ritsu (or Ricchan, as nicknamed by Yui) is the president of the light music club and plays a Yamaha Hipgig Drumset. She has an ambiguous yet upbeat personality, but often has trouble remembering important club activities and announcements, and gets constantly yelled at by Nodoka for forgetting to send in important forms. Ritsu is cheerful, often likes making jokes and is sarcastic most of the time. She usually brainstorms for ideas to earn more money and for the club's success. She says she chose to play the drums because they are "cool", but in reality, she admits that she has trouble playing instruments which involve intricate finger movements, such as the bass, guitar and keyboard. She is a childhood friend of Mio and will often tease her whenever she is cowering from something and has the opportunity to do so. Ritsu is always on the go and will stop at nothing for the success of the light music club. She has a younger brother.
Mio Akiyama (秋山 澪, Akiyama Mio)
Voiced by: Yōko Hikasa
Mio is a shy girl who is in the light music club and plays a left-handed, 3-Color Sunburst Fender Precision Bass (Fender Jazz Bass in the anime), with a tortoiseshell pickguard. She originally intended to join the literary club, but is forced into the light music club by her childhood friend and the club's drummer, Ritsu. She gets excellent grades in school, but is bad with listening to stories involving macabre experiences, and cowers whenever something gross is brought up. While she can be mature and strict sometimes, she gets embarrassed easily, and is often subject to teasing from Ritsu and Sawako, their club adviser. She cites that she chose bass since it is not the center of attention in the band, unlike the guitarist (though being the main vocalist somewhat negates this). Mio is more technical when it comes to music, and Yui often comes to her when she is in need of more guitar tutorials. She is the main vocalist in the group and also writes the songs, although they feature some odd lyrics like "Light and Fluffy Time". She is left-handed and becomes entranced whenever she sees left-handed instruments. Due to an unexpected accident in one of their live performances, a fan club for her is then formed (much to her dismay considering the circumstances surrounding it), whose founding member is the former student council president, who also stalks Mio.
Tsumugi Kotobuki (琴吹 紬, Kotobuki Tsumugi)
Voiced by: Minako Kotobuki
Tsumugi, often referred to as 'Mugi' by her friends, is a wealthy girl with a gentle and sweet personality who plays a Korg Triton Extreme 76 Key keyboard in the light music club. Tsumugi is considered a piano prodigy since she has been playing the piano since she was four and has experience in winning various piano contests. She is the daughter of a company president, and her family has several villas in various places around Japan (and even one in Finland, much to Ritsu, Azusa and Ui's surprise when they try to contact her at home). Since her father also owns a maid café, she often brings confectionery and an assortment of sweets and pastries to the club room, and she diligently makes tea with a tea set which is kept in their club room. Although she is a sweet and gentle girl, she is often weirdly entranced by the sight of two girls interacting closely together, sometimes imagining something more risqué in her head (both Mio and Ritsu find this awkward at times). She originally intends to join the choir club, but joins the light music club instead after receiving an invitation and encouragement from both Mio and Ritsu. Despite her being wealthy, she also tries her hand at a part-time job at a fast-food restaurant. While a lot of things do not bother her, she is fairly conscious about her weight like Mio, and she gets a bit anxious when her family's staff start spoiling her friends during villa visits.
Azusa Nakano (中野 梓, Nakano Azusa)
Voiced by: Ayana Taketatsu
Azusa is a new student who joins the light music club and plays a Fender Mustang electric guitar. She is in the same year and class as Ui and has quite a mysterious demeanor. She is a self-proclaimed novice guitarist who has been playing the guitar since she was in the fourth grade, and her parents are working in a jazz band. She often finds herself bewildered by the tea parties and cosplaying aspects of the club, when she would rather just practice and is curious on how the club is able to play so well despite their problems and lack of practice. However, she has a certain weakness for cakes and can be calmed down rather easily, sometimes by just being petted. She is constantly hugged by Yui and is nicknamed Azu-nyan after trying on a pair of cat ears and meowing. Despite this, Azusa is not too good with cats. In the band, she looks up to Mio the most due to her maturity and the fact that she is an experienced bassist. She even tries to give Mio chocolate on Valentine's Day. Since joining, Yui comes to her for advice on playing guitar, as well as maintenance.
Sawako Yamanaka (山中 さわ子, Yamanaka Sawako)
Voiced by: Asami Sanada
Sawako is the adviser for the wind instrument club at Yui's school. An alumna of the school and a former member of the light music club, she does not want people to find out that she was formerly a member of a heavy metal band, thus she covers up by being mild and gentle to her coworkers and especially to students. She is forced to be the adviser of the light music club, as Ritsu blackmails her after the girls learn of her past, though it is unknown whether she stopped being the adviser for the wind instrument club as the story progresses. Though she has a mature and gentle demeanor in the school, Sawako (affectionately addressed as "Sawa-chan" by both Ritsu and Yui) displays a totally different, completely authentic character when she is alone with the light music club. In reality, she is rather wild, lazy and quite an irresponsible teacher who enjoys dressing up the light music club in (sometimes embarrassing) cosplay costumes (like French maid uniforms), much to the dislike of Mio. She names the club band "After School Tea Time" (放課後ティータイム, Hōkago Tī Taimu) after the members take too long deciding on a name themselves (and to maintain the secrecy on her heavy-metal image). She once momentarily pitches in for Yui with her Gibson Flying V electric guitar (in the anime only). She becomes the girls' homeroom teacher in their third year, and puts all the band members (except Azusa, since she is a grade lower) in the same class, so she does not have to remember as many names.
Nodoka Manabe (真鍋 和, Manabe Nodoka)
Voiced by: Chika Fujitō
Nodoka is Yui's childhood friend and confidant who is a member of the school's student council. As a normal, well-mannered and intelligent girl, she is generally taken aback by the light music club's odd behavior, and easily gets annoyed with Ritsu whenever she forgets to fill in the club's application forms. She shares the same class as Mio in their second year, who appreciates her companionship tremendously, she being the only person Mio knows in her class. In her third year, she becomes the student council president and is also in the same class as the other third year club members.
Ui Hirasawa (平沢 憂, Hirasawa Ui)
Voiced by: Madoka Yonezawa
Ui is Yui's younger sister, who begins the story as a third-year junior high school student, but later enters the same school as her older sister in high school the following year. Unlike her older sister, Ui is mature, smart, responsible and handles household chores well, though she still shares a strong relationship with Yui. Despite being a year younger than Yui, she is nearly identical to her with her hair down and is even once able to fool the club. She has an extreme talent for playing the guitar, and became capable of playing with the rest of the light music club band after only a few days of practice. Ui is actually considered as the ultimate groupie for her sister's band and supports them with all her heart. She occasionally provides a narrative to the story. She is in the same class as Azusa and hangs out with her sometimes.
Jun Suzuki (鈴木 純, Suzuki Jun)
Voiced by: Yoriko Nagata
Jun is Azusa's and Ui's classmate who often hangs out with the latter. Ui tries to get her to join the light music club but ultimately fails due to a strange visit to the club room. She has a pet cat.
Megumi Sogabe (曽我部 恵, Sogabe Megumi)
Voiced by: Asumi Kodama
Megumi was the president of the student council before Nodoka succeeded her in her third year, and she is also the president of Mio's fan club. She stalks Mio during her last few days in high school because she wanted to see Mio one more time. The band offers her a song as a graduation gift. She can be seen in episodes six and eleven of the anime.
