Kazuki is a second year student of Ohbi Academy. He comes from an upper class family. Kazuki is the older brother of Mami and a relative of Yui. He is a childhood friend of Souta, Yui, and Yuko and were together since elementary school. Kazuki and Souta are members of the Boys' Light Music Club.
Kazuki loves The Beatles. He and Yui were in the same class during middle school. Kazuki refers to Souta as "Sou-chan". He was later revealed to be a talented composer. Kazuki is rather popular among girls.
Kira Kira: Curtain Call
Chapter 1: Here Today, Go Tomorrow
After Souta ran away from his senior Tanabe, he phoned Kazuki to meet him at the park. Souta voiced his wish to form his own band. Kazuki reminded Souta to dye his hair back to black.
Souta and Kazuki were going to perform with the Boys' Light Music Club during the Ohbi Cultural Festival. Kazuki invited Souta to practice but their seniors left early to study. After school, Kazuki invited Souta to buy music CDs. At Kazuki's house, they met his sister Mami who lost her keys. Souta and Kazuki helped her look and Souta enjoyed teasing Mami.
Chapter 2: I'm a Rock'n'Roller
Souta formed the Super Rock'n'Rollers with Kazuki, Akihiro, and Shouki to compete at the upcoming band competition. At their first practice, Kazuki tended to play too slowly. Kazuki helped write their original song and designed the logo.
Chapter 3: Chain Saw
Kazuki started to fall down frequently. He approached Souta just before the band competition to explain that he had contracted amyotrophic lateral sclerosis the previous year. It is an incurable disease which will waste away neurons, causing loss of control over muscles.
Souta couldn't concentrate on the performance and played their first song poorly. Kazuki then punched Souta and begged him to play well for his sake as his last time on stage. Souta then revived and played well. Super Rock'n'Rollers disbanded immediately after that.
The next Summer, Kazuki and Mami invited Souta to a bar. Kazuki gave Souta his guitar, reasoning that he can no longer play again and that it would serve Souta well. Souta announced that he was going to quit school. Kazuki tried to reveal that Mami liked Souta but she yelled over him.
Kazuki's legs failed and he could no longer walk. He became hospitalized and Souta and Mami visits him frequently.
Chapter 2: Don't Stop Dreaming
Mami revealed that Kazuki had been writing songs. He would hum to her and she would record it and write them down.
Chie brought Kazuki to the park. Kazuki explained to Murakami that he was afraid of his impending end but he was determined to live out the rest of his life the best he could. Souta then approached them to bring Kazuki back to the hospital.
Chapter 3: Let's Do It, The Music
Souta revealed Happy Cycle Mania's 5th year anniversary event to Kazuki. Kazuki composed a new song and Souta wanted to perform it at the event.
Kazuki uses a red colored Yamaha SG1000 or SG2000 (both models look the same, though the SG1000 is noted to be lighter than the SG2000).
- The "-chan" honorific is usually used for or by girls. Kazuki's use of "-chan" further propels his effeminate disposition.