Always looking for fun, Yui is fearless; anxiety and stage fright are unknown to her. She likes everything cute and makes a lot of physical contact like holding hands or hugging. She also loves everything sweet (that's why Ritsu gave her a Alias "Lazy Fairy"). Sweets that Mugi brings are Yui's power source. Her physical constitution is such that she does not gain weight no matter how much she eats. She can't stand being hot or cold, so she spends the winter under the kotatsu (a knee-height table with an electric foot-warmer installed inside on the top board, which is used with a coverlet during winter) and rolls around on the floor in the summer in front of the fan, to keep cool. Her grades are always on the verge of failing exept for the fine arts in which she is exceeding; sometimes she is the only person in her class who needs to retake a test, other times she manages to avoid failing all of her subjects by a one point margin. She has an average figure. Yui lives in a family of four with her younger sister Ui and both parents. Her parents are a "lovey-dovey" couple and often go on trips together, leaving both daughters behind.
Main character, lead guitarist, lead vocalist. Having misunderstood that "light music" equals to "easy music" (like whistling), she joined the Light Music Club and picked up guitar with absolutely no prior experience. She cannot do more than one thing at a time, but to make up for that she can be highly focused on a particular subject and once started, can advance quite sustantially. However, whenever she learns something, she forgets something else. Yui is the type of person who doesn't read manuals and relies on her own intuition and self-taught approaches. She also does not remember any of the musical terminology. She possesses perfect pitch and is musically gifted. She is able to tune her guitar without a tuner, but she does not appear to make the best of her ability. Yui is relatively determined and competitive, but at the same time she feels comfortable depending on the help of a few good people like Ui, Nodoka, Mio and Azusa.
Perhaps Yui's most prominent trait, however, is that she is a romantic and kind-hearted dreamer who cherishes the people the people in her life, expressed most frequently in openly affectionate hugs that she freely gives out. For the people that she loves, she is capable of accomplishing deeds far exceeding her normal intelligence, determination and talent, such as simultaneously studying for finals while rehearsing for a concert to win a vacation for the neighborhood granny who has been kind to her.
Yui is a teenager of below average height of 5'1", with brown eyes and thick medium brown hair at shoulder length, often accessorized mostly with two yellow pins.
Pants over skirts. Yui is relatively fashion-concious and prefers styles featured in teen magazines. She also wears casual clothes such as shorts and t-shirts at home.
Sakuragaoka High Uniform
|thumb|link=http://images4.wikia.nocookie.net/__cb20121014121648/k-on/images/e/e3/Yui_profile_picture.pngthumb|link=http://images4.wikia.nocookie.net/__cb20121014121648/k-on/images/e/e3/Yui_profile_picture.png||Like all Sakuragaoka High students, Yui has to wear school uniforms. The Sakuragaoka Uniform Yui wears has a navy blue blazer, solid white buttoned shirt (under blazer), a aqua blue ribbon (different colors for different student years), light steel blue skirt, black stockings (sometimes long white socks) and maroon shoes.|
Don't say "lazy" Attire
|thumb|link=http://images1.wikia.nocookie.net/__cb20121219141160/k-on/images/0/0d/Yui_Dont_Say_Lazy.pngthumb|link=http://images1.wikia.nocookie.net/__cb20121219141160/k-on/images/0/0d/Yui_Dont_Say_Lazy.png||Yui's Don't say "lazy" attire is a white knee height dress with black frills. Large celeste (light blue colors) beads used as shoulder straps. Her right arm is wearing a solid black arm glove. Vertical black and white striped stocking. A pair of white high heeled shoes with a black and burgundy bead. Yui's hair is done more shaggy and accessorized with a white frilled flower with a large purple bead.|
|thumb|link=http://images2.wikia.nocookie.net/__cb20121219141418/k-on/images/8/85/Yui_listen_attire.pngthumb|link=http://images2.wikia.nocookie.net/__cb20121219141418/k-on/images/8/85/Yui_listen_attire.png||In Listen!!, Yui wears a black shirt under a white shirt with a washed out kiss mark over a blue lightning bolt print. Blue jeans, maroon boots with black laces. Yui is accessorized with green hoop earings and bracelet. Yui parts her bangs to the left without her two yellow pins, leaving her bangs covering her left eye.|
NO, Thank You!
|thumb|link=http://images2.wikia.nocookie.net/__cb20121116045229/k-on/images/1/14/Yui_No_Thank_You.pngthumb|link=http://images2.wikia.nocookie.net/__cb20121116045229/k-on/images/1/14/Yui_No_Thank_You.png||In NO, Thank You!, Yui's attire is similar to any school uniform dress code. Her attire is close similar to the Sakuragaoka High uniform- navy blue blazer, white buttoned shirt (under blazer), and the maroon shoes. The only parts different is the logo pinned to her blazer and the plaid grey skirt.|
|thumb|link=http://images2.wikia.nocookie.net/__cb20121219141654/k-on/images/3/35/Yui_No_Thank_You_2.pngthumb|link=http://images2.wikia.nocookie.net/__cb20121219141654/k-on/images/3/35/Yui_No_Thank_You_2.png||Yui's second attire in NO, Thank You! She wears a plain solid white tank top with a blue pin near her right shoulder, and a red knee height skirt.|