|Height||155 cm (5'1")|
|Birthday||February 13 (Aquarius)|
|Occupation||High School Student (first year)|
|School||Kitauji High School|
|Light Novel||Volume 1, Chapter 1|
Hazuki Katou (加藤 葉月 Katō Hazuki) is one of the main characters of the Hibike! Euphonium series. She is Kumiko's classmate and looks a bit suntanned because she belonged to the tennis team when she was a junior high school student. Hazuki plays the tuba.
Hazuki has the appearance of a young girl, with short, straight brown hair, that curls at the bottom, and gold-hazel colored eyes. She has a red-pinkish hair clip which she accessorises her hair with. She wears the normal Kitauji High School female student uniform for first-year students.
Hazuki is a bright and perky mood-maker and also very energetic and cheerful. She is almost always seen with a smile on her face, and she can quickly become familiar with people, which is seen in Episode 1 when she refers to Kumiko as "Kumiko-chan", even though she just met her. She is a friendly girl who talks innocently and she is the type of person who prefers standing out to supporting others.
Hazuki was on the tennis team in junior high school, and is a beginner in music. She admired the trumpet and joined the concert band, but ends up playing the tuba.
Hazuki makes her first appearance in Welcome, High School, where she becomes one of Kumiko's first friends upon entering Kitauji High School. Just after meeting Kumiko, she starts calling her by her first name and telling her to do the same thing with her too, which quite shocks Kumiko.
Kumiko and Hazuki get along very well, even though Kumiko normally does not mix with sport-orientated people. Hazuki treasures Kumiko as a very good and close friends, and they support each other and they are almost always seen together (with Sapphire). They can freely talk about various topics with each other and they trust each other. They are good terms.
Even though Sapphire was very shy from the beginning, she became more social and cheerful from being with Hazuki and Kumiko. Sapphire and Hazuki are also great friends and Sapphire is one of Hazuki's first friends in Kitauji High. Hazuki trust Sapphire very much and can tell her about all kind of things, and they support and care for each other. They have a very good and friendly bond.
At first, Hazuki didn't really have any interest in Shuuichi, and only saw him as ''Kumiko's friend''. However, after learning a little more about him, Hazuki gradually becomes more interested in him. And, towards the end of the seventh episode where Shuuichi helped Hazuki, she fell in love with him. Kumiko and Sapphire find out about this and becomes shocked, especially Kumiko. Also, Kumiko makes Hazuki go the Agata Festival with Shuuichi, which they do, even though Shuuichi wanted to ask Kumiko.
While the two were talking, Hazuki confessed that she liked him. Shuuichi, however, didn't feel the same, and told her that he only saw her as a friend and that he already has another person he likes. Hazuki realizes it's Kumiko, and says that she is going to support him to be with Kumiko instead. They became a little bit distant after this event, but they are still on good terms.
- Hazuki (葉月) is the old Japanese word for the month of August. It is also a Japanese surname and given a name.
- Riko often encourages Hazuki to do her best.
- Kumiko, Hazuki, and Midori are all in Year 1, Class 3 in the book series.
- Hazuki is from Higashichu Lower School as the book series states.
- In the book, Hazuki dyed her hair.
- Hazuki's homeroom teacher is Michie Matsumoto.
- In the book series, Hazuki has/had a trumpet charm on her bookbag.
- In the book, she is said to be athletic because she was tan.
- Hazuki was originally thinking about playing the Trumpet in the book.