Age: 14-15
Birthday: July 4

Kaori Miyazono is one of the main protagonists of Shigatsu wa Kimi no Uso. She is a violinist who helps Kousei Arima return to the piano world after his mother's death.

Kaori Miyazono is a free-spirited violinist whose playing style reflects on her personality. She is independent, unpredictable, and short-tempered. It is also touched upon that she is passive aggressive at times. Kaori likes to depend on herself and only herself and can be seen as more of a support for others.

While considered a really sloppy violin player from a technical standpoint, such as not following music score sheets the way they are written, Kaori is an amazing violinist. Noted by one of the judges at Towa Hall during the first competition of the series, her pure abilities far exceed the others in the competition. She wields a free spirited style of performance that emphasizes emotions and artistry over the pure mechanics of music, such playing to specific tempos and dynamics originally intended by the composer. Her style of music is what rekindles Kousei's passion for the piano and inspires him to redefine himself as a musician.

In addition, she has the ability to play the melodica and has had some experience playing the piano.

When Kaori was five-years-old, her piano class went to see a music recital, there, she first saw Kousei. From the moment he touched the keys and started playing, she was immediately inspired by the spirit in his music. Kaori was originally an aspiring pianist herself, however later decided that she would become a violinist and have Kousei play with her. Kaori was always a physically weak child, and underwent many surgeries. Over time, her hospitalisations became more frequent and prolonged.

One day, she saw her parents crying in the hospital as they realized she didn't have a lot of time left. Because of this, she decided to live a full and happy life before passing away. She put on the contacts which she never had the courage to wear, ate a lot and ignored the aspect of her appearance and played the music the way she wanted to and not how everyone else wanted her to. Then, she told a lie.
It is later revealed that she wasn't able to perform with Kousei after she fell and hit her head at home, resulting in her bleeding and passing out. After this incident, Kousei rushed to visit Kaori after hearing from Tsubaki that she was hospitalised again.

It later comes to a point where it becomes obvious her health is deteriorating rapidly and she can no longer hide her illness from her friends. She is shown at one stage that her illness has caused bouts of paralysis in her legs, where she suddenly falls to the ground while walking down the hallway in the hospital, unable to make herself stand up.

As Kaori's final days were coming, she wrote a farewell letter to Kousei. On February 18, the day of Kousei's piano competition, Kaori had her operation. At her funeral, her mother gave the letter she wrote to Kousei.
After witnessing Kousei performing at the recital, she was awestruck by him and immediately gave up on playing the piano as she wants Kousei to play for her. A few years later, Kaori finally got to meet with Kousei. After getting to know each other, they both realised that they as musicians, have a lot in common. Kaori first found out that Kousei became tone-deaf when he's concentrating on playing the piano when she asked him to play 'Twinkle Twinkle Little Star' in a cafe. She then demanded Kousei to be her accompanist. Although reluctant at first, Kousei finally accepted when Kaori begged him to support her in that "moment that she's about to lose heart." Their relationship gradually strengthens and they start spending more and more time together, especially in the music room. Kousei found himself falling in love with Kaori, but held back because she was Watari's love interest.

At the end of the series after Kaori's death, it is revealed that she always had a crush on Kousei and always loved him since she was young, and because she knew Tsubaki also loved Kousei and would never introduce her to him if she found out, thus having to lie about her faked crush on Watari just so she could approach Kousei.
(Source: Shigatsu wa Kimi no Uso Wikia)