Profile

Birthday: November 27
Sign: Sagittarius
Height: 156cm
Weight: 50kg
Blood type: O

Favorite Music: Yui doesn't follow any particular style, and isn't picky. If she likes it, it's okay.
Experience with musical instruments: None.
Family Structure: Family of four, both parents and younger sister Ui. Her father works for a trading company, and tends to be absent with overseas assignments. Her mother often goes overseas with him, so the two daughters have many opportunities to spend time together.
Dwelling: Single-family detatched home.
Commute to School: Walks.
Preferences in Clothing: Pants over skirts. She is relatively fashion-conscious and likes styles featured in teen magazines. She wears casual clothes such as shorts and t-shirts at home.
Her Room: Clean, because Ui cleans it. Yui likes cute things, and keeps stuffed toys in her room. The room is painted in girly pastel and pink tones.
Favorite Food: Anything, as long as it's sweet and tasty.
Best Subjects: None.
Worst Subjects: Everything
Physical Exercise: She can do it, but hates getting tired.
Way to Pass Time When Alone: Lazing around at home.
Weaknesses and Dislikes: Studying.

Main character of K-ON!. She is the lead guitarist and lead vocalist in Houkago Teatime. She plays a Gibson Les Paul Standard, in Heritage Cherry Sunburst, nicknamed Giita (ギータ). She joined the Light Music Club, thinking that "light music" meant "easy music" (like whistling or playing the castanets), and picked up the guitar with absolutely no prior experience.

She is easy going, clumsy, and spaces out often. She cannot do more than one thing at a time, but has amazing concentration when she focuses on one subject, achieving outstanding results. However, when she learns something, she usually forgets something else. She is easily distracted by trivialities (usually, cute and adorable things), but is very devoted to her band, and practices very hard when she has to.

Yui relies on her own intuition and self-taught approaches, and doesn't remember any musical terminology (much to the amazement of Mio and Azusa). She has perfect pitch, and is able to tune her guitar without a tuner.

She is fearless, and doesn't feel anxiety or stage fright.

She likes cute things and physical contact (particularly with Ui, and the victim of her skinship, Azusa). She loves sweet things, and is powered by the sweets that Mugi brings, but doesn't gain weight regardless of how much she eats.

She can't stand being either hot or cold, so she spends her winters under the kotatsu, and her summers rolling around the floor with a fan because she also dislikes the air-conditioner.

Yui is quite determined and competitive when she is fired up, but doesn't mind relying on other people - usually Mio, Nodoka, or Ui.

Sources:
http://myanimelist.net/character/19565/Yui_Hirasawa