Kazuki Hiroshima is one of the main characters in FUTURE, and is a co-founder of their band. He is a third-year in Fuchigami International High School, and his sister, Harumi Hiroshima, is a second-year. Kazuki lives with Harumi and their parents. He doesn't seem to have many friends outside of their band, other than Alice Collingwood.
Kazuki has brown skin and medium-small dark brown eyes. He has short orange hair, which is usually side-parted, with his bangs going over half of his right eye.
Kazuki's outfit consists of his school's uniform - a white collared shirt with a blue tie, a navy blue coat, and black pants with a navy belt. His everyday outfit often consists of a plain long-sleeved shirt with a coat or jacket and jeans.
Kazuki is known in the school to be quiet, easy to annoy and "cold" towards other people. He doesn't seem to care much for his grades or to show up at school in general. He starts to attend school more regularly because of the band and throughout the show, he becomes softer towards his band members and other classmates, like Alice. Kazuki also seems to have a goofy and naughty side to him, cracking jokes when he wants to, and maybe even pulling pranks. For example, he came up with the famous, school-wide nickname, "Boogereyes" for Takahashi-Sensei, a teacher at his school who has yellow-green eyes.