Kazuki is an outgoing person and is extremely friendly to others. He has little sense of social boundary. During his time in middle school, he was in the track team but pulled out to play the trumpet in the school band.
He explained to Kahoko that one day he went to the rooftop to have lunch, however when he arrived, there was a female senior playing the trumpet. He was amazed at how she played. Soon after, she was there everytime he went to the place to have his lunch. Later, she brought a trumpet she borrowed from the school’s music room. This finally allowed him to have a try on playing the trumpet. Nevertheless, at that time, he already joined the school’s track team and he was reluctant to leave and join the school band. However, in the end he had his friend’s support and quit the track team.
Kazuki has an enormous appetite, as he is constantly eating. He quickly befriends Kahoko. Because of him, Kahoko learned the true meaning of music, that it is enjoyed by everyone. After that Kahoko began to love and enjoy music better. In the middle of the series, he starts to call Kahoko "Kaho-chan", instead of the usual "Hino-chan", thus suggesting he has a rather obvious crush on her.
He’s also a member of the Orchestra Club.
He has an elder brother named Haruki.