|Yui Hirasawa is the eldest daughter of the Hirasawa family. Ui Hirasawa, her only sibling, is a year younger, and both share a close, affectionate bond. Because their parents travelled often on business, Yui was usually cared for by Ui, the more mature, albeit younger one. On a Christmas early in their childhood, Yui tried "fulfilling" Ui's wish for a "white Christmas" by placing a pillow's stuffing onto a tree in front of their home. Naturally, her actions earned heavy scoldings from their father.
Yui also grew close to Nodaka Manabe during early childhood. She first approached Nodoka in kindergarten, suggesting they draw pictures together. After Nodoka drew a delicious-looking apple, Yui thought that the crayon would be as delicious as the drawn apple seemed, and tried eating it. Nodoka managed to stop her, and both have been close friends since. They always attended the classes in school, and eventually, Nodoka became used to helping Yui despite all the trouble Yui caused her, like forgetting to buy the ingredient she was tasked with for a cooking lesson.
From an early age, Yui also build a strong connection to their kind neighbour Tomi Ichimonji.
After graduating from Junior High School, she was accepted into the Sakuragaoka High School.
On the first day of her high school career, Yui got the time wrong, thinking she was late for school, and started rushing towards her new school, leaving her sister behind confused. Upon arriving at the school, she got excited about the thought of being a high school student now. After a while, she ponders about what club she should join and comes to the conclusion to choose the Light Music Club. Later after her decision, when asked by Nodoka why she chose the Light Music Club, she expresses how it would be easy for her to be in the club, since she does know how to play the castanets, having a flashback from when she was in kindergarten playing the aforementioned instrument.
Yui then visits the Teacher's Lounge to help Ms. Yamanaka get to their class but, due to her clumsy behavior and having her attention be on two other students, accidentally drops Yamanaka's papers on the floor and hits her head on the desk before shakenly bringing them to the classroom. Soon, Yui decides to finally visit the Music Room where the Light Music Club is at, feeling a bit nervous at first and having exaggerated thoughts about the club, before she is greeted by the club's president, Ritsu Tainaka, who was one of the girls she saw earlier at the Teacher's Lounge. With Ritsu overjoyed to finally meet her, Yui is then introduced to the other members of the club, bassist Mio Akiyama, and keyboardist Tsumugi Kotobuki.
Though at first the club was excited to meet her, due to expecting her to be a guitar prodigy, Yui admits to not knowing how to play a guitar or any other instrument except for the castanets. However, the club decides to play a song they made themselves, where Yui gives a rather blunt reaction to. Despite not knowing how to play a guitar, Yui joins the club and promises to learn how to play a guitar soon.
After being accepted into the Light Music Club, Yui joins Mio, Ritsu and Mugi in the music room. Later, Mio reminds her that she has to buy a guitar as soon as possible so that she can begin practicing on it and after school, she gets a ¥50,000 advance on her allowance. Yui then goes off to meet the others the next day to buy a guitar, but on the way she becomes distracted by a few things, becoming late as a result. They arrive in a music store where Yui spots a particular guitar she immediately becomes attracted to; a Gibson Les Paul.
To her and the others' surprise, the guitar is too expensive for her to afford. The rest of the club then decided to take part-time jobs to help her afford it, with Yui thanking them all. For the next two days, she and others count automobiles for a traffic survey, but she then begins to feel bad to having to rely on the others to help her and decides to give their money back and buy a cheaper guitar. Yui and the others return to the music store the next day and, despite what she said, she feels upset after looking at the guitar she had wanted to buy. To her, Mio and Ritsu's complete surprise, Mugi was able to have an employee in the store to lower the price of the Les Paul to one that Yui can afford, to Yui's excitement.
The next day, Yui happily presents her new guitar to the rest of her friends, but still needs to learn how to play it.
Yui is sitting her classroom with her club application form, thinking of what kind of club she wants to join in for her new high school life. Yui's childhood friend, Nodoka Manabe, asks her what she is thinking about and Yui replies that she still hasn't decided what club to join to Nodoka's shock, telling her that it has been two weeks since they started high school.
Not wanting to become a NEET, Yui decides to join the Light Music Club and is asked by Nodoka what kind of instrument will she be playing in the club with Yui responding that she isn't sure. Soon after, Yui goes to visit the light music club's clubroom, intending to quit but wonders what kind of people are in the club, the thought of which scares her. Before she enters, the president of the club, Ritsu Tainaka, asks her what she is doing outside their clubroom and then asks her if she is Yui Hirasawa, excitedly greeting her and then introducing her to the other club members, thinking that Yui is an amazing guitarist to Yui's dismay. Ritsu says that they just established the club recently but happily thanks her for joining their club, but Yui tells the girl that she was intending to quit the club. Another one of the members, Mio Akiyama, points out to Yui that she may have had an interest in music which is possibly why she decided to join. Ritsu then opts to play a piece of music they made to her which might help her decide if she wants to continue in joining them or not, to Yui's surprise.
After the performance, Ritsu asks her of what she thought and Yui bluntly says that they weren't all that good. Either way, Yui eventually makes up her mind and joins the club, to the other members' joy. Yui, however, reminds them that she still can't play any instrument. Tsumugi Kotobuki gives her the idea of picking up a guitar as their club has no guitarist yet, but Yui finds the role being difficult. Ritsu, however, offers to have her, Mio and Tsumugi help her practice on one soon. The next day, Yui tells Nodoka that she finally joined the light music club, to Nodoka's surprise, saying that she joined as an actual member and will become the club's guitarist, stating the other members will teach her how to play one.
Some time after, Yui goes to the clubroom and introduces each of the following members of the club: the bassist and very delicate, Mio Akiyama, the wealthy, cheery keyboardist, Tsumugi Kotobuki and the club's lively president and drummer, Ritsu Tainaka. Mio asks Yui if she has already managed to buy a guitar with Yui responding that she forget that is the designated guitarist for the club. When told about the potential price of a cheap guitar, Yui asks the other members if they could lend her some money which they all kindly deny. However, the next day, Yui is together with the group to check out the local music store to see if she can find a guitar that she may like. While looking through the store, Yui finds a guitar she becomes immediately attached to but unfortunately learns that the guitar costs 150,000 yen. Thanks to Mugi being recognized by the staff as the daughter of the owner of the store, the price is lowered to an affordable 50,000 yen and Yui buys it. Later at her room, Yui tries on the guitar and ends up sleeping next to it the next morning.